§ 1.

In the living human body, the healthy
functions of which constitute the exclusive object
of the science of Physiology, there occur three
things worthy of our immediate attention and
regard^*; namely,

The Solids, or parts containing;

The Fluids, or parts contained within the solids;

And lastly, the Vital Energies, which in the
consideration of the science of physiology, consti-
tute the most interesting and important object of
our regard. It is in consequence of these energies
that the solids are rendered alive to the impulse of
the fluids, endued with a power to propel the same,
and also to perform a variety of other motions.
It must however be observed, that these energies
are not incommunicably excluded even from some
of the fluids themselves: on the whole, they ap-
pear to constitute the essence or supreme charac-
teristic of an organised body.

§ 2.

But although these three objects have been with
propriety considered as distinct from each other,
and may therefore be separately enumerated on
the present occasion, they are notwithstanding in
the living body, which is alone the exclusive sub-
ject of physiology, so intimately connected toge-
ther, that it is scarcely possible to form even a
conception of one without at the same time em-
bracing the others.

The most pure and limpid fluids of our body
abound with animal earth: on the other hand,
though our solids may appear to us completely
destitute of liquid matter, yet, besides the circum-
stance of their originating from the fluids as their
matrix or primary source, they contain in their
composition an evident quantity of moisture:
lastly, if we be not deceived, it is certainly true
that there exists scarcely a fibril in the living
body which does not possess, in a higher or lower
degree, a vital energy inherent in itself.

§ 3.

We now proceed to treat of each of those three
objects separately and in order: and first of the
fluids; as constituting by far the greatest, and
what may be emphatically called the first-born
part of our bodies.

§ 4.

All the different fluids of our body,
may with propriety be thrown into three leading
classes.

These are, I. The Crude or unassimilised fluid,
consisting chiefly of the chyle contained in the
primae viae, and destined for conversion into blood;
to which may also be added, that fluid received
by absorption from the external superficies of the
body, and conveyed to the same receptacle with
the former.

II. The blood itself;

And Lastly, the secreted fluid, or that formed
from the volume of blood by the animal process,
called secretion: the fluids prepared by this pro-
cess are destined, some of them, to be retained in
our body, to serve further purposes in the animal
economy; and others, to be eliminated from our
system, as wholly excrementitious.

§ 5.

Of the first and third of those classes we will
speak on a future occasion, when we come to treat
of chylification, and of secretion, together with the
other functions to which those fluids are respec-
tively related. Let us now proceed to the consi-
deration of the blood, that most important, that
primary, and truly vital liquid, which may with the
greatest propriety be called, the living fountain
of all the other fluids; as being that into which
the crude fluid is converted; and from which all
[Seite 5] the secreted fluids derive their origin; and which
(a few parts of the body excepted, such as the
epidermis, the tunica arachnoidea, the amnion,
the vitreous substance, or enamel, of the teeth,
&c.) flows uniformly through every even the
most minute and fine spun parts of the inexplicable
texture of our system.

§ 6.

The blood is a liquid sui generis, of a well
known colour, more or less intense: it is glutin-
ous and warm to the touch: the formation of this
liquid has hitherto been ranked among the arcana
of nature, as it has never been successfully imi-
tated by any process of art.

§ 7.

This vital liquid when recently drawn from a
living subject, and received into a vessel, exhibits
in a very obvious manner the following remark-
able phenomena:

In the first place, while it is yet warm, a subtle
halitus ascends from it, which being collected in a
receiver, forms small pellucid globules, similar in
appearance to drops of dew; it is of an aqueous
nature, resembling not a little common fountain
water, except that it emits a peculiar nidorous
smell, (still more considerable in the blood of car-
[Seite 6] nivorous animals) and which may be aptly called
the animal odour; such, for example, as arises
from fresh urine, or from the thoracic and abdo-
minal cavities of a dead subject recently opened.
Of this aqueous liquor a considerable quantity re-
mains in a state of mixture with the other consti-
tuent parts of the blood, which shall be hereafter
mentioned.

§ 8.

In the mean while, as the blood contained in
the vessel suffers a gradual reduction of tempera-
ture, it begins to separate into two parts. A
coagulum is first formed, from the superficies and
sides of which, there presently exsudes a liquor
of an intermediate shade between pale yellow,
and evanescent red, which they call the serum of
the blood; in proportion as this liquor accumu-
lates by exsudation, a corresponding diminution is
observable in the volume of the coagulum itself;
the coagulum thus reduced in size has been dis-
tinguished by the name of crassamentum, as also
by those of the liver, and placenta of the blood,
from a resemblance, in point of colour and fran-
gibility of texture, supposed to exist between it
and these two bodies; it has been likewise called
the island, from the circumstance of its being held
in a natant or floating state in the surrounding
serum.

§ 9.

This crassamentum itself, by a delicate treatment,
such as gentle agitation or frequent ablutions in
water, may be again separated into two constituent
parts, viz. the cruor, which imparts the red co-
lour to the whole mass of blood, and which by
ablution is carried off from the lymph, the other
and more substantial part, and which, therefore,
is called the basis of the crassamentum; that the
cruor retains for this basis a much stronger af-
finity than the serum possesses, is sufficiently ob-
vious from this circumstance, that the cruor and
basis cannot be disparted unless by the interpo-
sition of a certain degree of force. The lymph
itself being robbed of the cruor, becomes more and
more pale until it finally assumes the appearance of
a white and considerably tenaceous coagulum.

§ 10.

Such then appears to be the four principal con-
stituent parts of the blood, – viz. the watery
halitus; the serum; the cruor, or red globules;
and the coagulable lymph; which several parts,
as long as they retain their native degree of vital
temperature, continue in a state of the most
equable mixture, constituting an uniform and
homogeneous fluid.

It will now be proper to enter into a more mi-
nute consideration of those three portions of the
blood which stand last in the above enumeration:
As to the aqueous exhalation which we have men-
tioned, it does not appear of sufficient importance
to claim any further attention; indeed as it is also
discovered in other parts of the body, it cannot
be considered as proper to the blood alone, any
more than the air which this viral fluid contains,
and on which we will state a few observations in
a subsequent part of this section.

§ 11.

The serum is a liquid of such a gelatinous nature
as to impart to the whole mass of the blood the
chief part of its viscosity or gluey consistence: it
very much resembles, in all its properties, the al-
bumen or white of eggs; when subjected to the
action of a temperature equal to the 150th degree
on the scale of Fahrenheit’s thermometer, it pas-
ses into a coagulum, white and easily broken
down, analogous to the white of eggs in a boiled
state; it also suffers a similar change, according
to the experiments of the celebrated Moscati, if
it be mixed with a quantity of quick lime, though
in this case the coagulation proceeds much more
slowly, and is not completed till after the twen-
tieth hour. But if the serum be dried with a
gentle heat, and left wholly undisturbed, it is
[Seite 9] converted into a firm pellucid mass, similar in its
external appearance to gum arabic, which in a
gradual manner, like the dried white of eggs,
cracks and forms over its surface numerous sulci
or fissures running in a somewhat spiral direction,
and exhibiting a very singular appearance.

§ 12.

Besides those other properties of the serum
already mentioned, there is one highly worthy
our consideration, to which my attention was first
called by the experiments of the illustrious
Priestley^*; but my belief of which has since
been fully confirmed by repeated observations of
my own, viz. the facility with which the air, sur-
rounding a vessel filled with blood, is able to act
through the medium of the serum or the crassa-
mentum, though deeply covered by the former, in
such a manner as to produce a very remarkable
change in the colour of the latter, whereas, on
the other hand, the same action of the air would
be very much impeded, if not entirely prevented,
if instead of the serum, the crassamentum were
covered with any foreign liquid, such as water,
or oil, &c. or even with any other fluid of the
human body itself, as the saliva or urine.

§ 13.

The cruor constitutes another very striking and
important part of the blood, and is a source of
many singularities, whether we consider the
colour and figure of its particles, or the elemen-
tary parts into which it is resolved when subjected
to the action of an intense heat. It appears to
deserve a place among the most elaborate juices
of the body, as it seldom appears in the tender
foetus previously to the fourth week after concep-
tion, nor in the nascent young of gallinaceous
fowls till the fortieth hour of incubation. After
profuse hemorrhages it likewise appears to be re-
placed by the powers of the system, with much
more difficulty than the other constituent portions
of the blood.

§ 14.

It consists of globules, first observed by Leeu-
wenhoek. In blood recently drawn they are al-
ways present, of a constant, uniform figure, and
of an equable magnitude; which circumstances,
added to the further consideration, that in no
other fluid (milk alone excepted, the particles of
which are somewhat analogous), are similar
bodies to be met with, leave not a shadow of
doubt, but that those globules form a part very
obviously and essentially different from the other
constituent portions of the blood, though at the
[Seite 11] same time the formation of those globular bodies
themselves appears in reality to be much more
simple than some celebrated characters would in-
duce us to believe. For to pass over in silence
the complexity of the sixfold form fictitiously be-
stowed on them by Leeuwenhoek, neither the an-
nular figure attributed to them by the illustrious
de la Torre, nor the form of vesicles enclosing an
opaque nucleous, such as Hewson apprehended he
discovered in them, have appeared to me to be
well founded^*. In my observations, indeed, I
have been able to detect nothing more than bodies
of a simple spherical appearance, and, if I am not
deceived, of a solid gelatinous consistence. I have
not, indeed, absolutely denied the lenticular figure
bestowed on them by some observers: I dare not,
however, venture to assert, that I have been so
fortunate as to observe it.

It has been a subject of controversy whether or
not they can alter their figure when it becomes
necessary for them to pass through a vessel of a
very narrow diameter. I am inclined to believe,
in conformity to the opinion of that accurate
observer Reichel that under the above circum-
stances, they do actually change their spherical
for an oval figure, and again resume their former
[Seite 12] globular shape, when they advance into vessels
sufficiently capacious; though I must confess, I
never had the happiness to be a spectator of this
interesting phenomenon.

This spherical figure of the globules is never
perceived unless in the blood circulating in the
vessels of a living animal, or in that which is re-
cently drawn; they lose all regularity of form in
process of time, and appear to dissolve, as it were,
and again unite with each other into one uniform
shapeless mass.

§ 15.

Physiologists differ in determining the size of
the globules of the blood. Hales reckons them
equal in diameter to the 1/3240th part of an inch.
Senac estimates their diameter at about the 1/3300th
part of the same measure, while others again en-
tertain different opinions.

§ 16.

Their colour is red, and therefore the beautiful
crimson cast of the whole mass of blood appears
to be evidently derived from them. The intensity
of this colour changes with a multiplicity of vary-
ing circumstances; it is more pale in animals which
are too sparingly nourished, or in such as have
suffered profuse hemorrhages. The blood con-
[Seite 13] tained in the arteries is more florid, together with
that which has been subjected to the action of
atmospheric, but more especially, that which has
been exposed to dephlogisticated air; while venous
blood is more obscure, as well as that which has
been acted on by fixed or inflammable air.

§ 17.

Upon the whole, the causes, which augment
the quantity of the red globules in general, and
also heighten the intensity of their colour, are
sufficiently evident: but to discover from what
secret source their disposition to this crimson dye
is originally derived, is a matter of Herculean
difficulty indeed. Haller ascribed it to the pre-
sence of crocus martis, because the blood abounds
more with iron than the bones, or other parts of
the body, although the quantity contained, even
in the blood itself, is very small; and although
authors differ astonishingly in their attempts to
ascertain it. Thus, for instance, Menghinus esti-
mated its relative proportion to the whole mass of
the blood, to be as 1 to 110; whereas, the illus-
trious Rhades calculated it to be only as 1 to 427;
and again, in some future experiments, to be no
more than as 1 to 503, &c.

On the present subject it seems proper to make
the following observation; viz. that no iron can
[Seite 14] be discovered in the cruor of the blood unless it
be previously calcined; whereas, on the other
hand, when it was dried with a gentle heat, and
reduced to the most impalpable powder, I could
not observe a single particle of it attracted by the
magnet, whether the experiment was made in
water, or in that most fluid of all vehicles, quick-
silver.

§ 18.

We now come to the consideration of that con-
stituent part of the mass of blood, which stands
last in our order of enumeration, viz. the Lymph;
which is by some called the basis of the crassamen-
tum, by others, the mucous or glutinous part,
and by others, the fibrous portion of the blood.

This, in former times, was very erroneously
confounded with the serum, from which it is not-
withstanding very widely different, in all its essen-
tial properties. When the lymph is exposed to the
action of air, especially of such as is of a low tem-
perature, it is immediately coagulated; but by the
admixture of quicklime, (which has been already
said (§ 11.) to have the power of coagulating
serum), it is preserved in a fluid state; or, even
though it be already coagulated, yet, by the
addition of this substance, it is again immediately
resolved.

§ 19.

We have already touched on the methods, by
which this part of the blood may be separated
from the cruor (§ 9.). It is also by other artifi-
cial methods, such as whipping or agitating the
blood with small twigs, induced to assume the
appearance of a membrane, which has been named
after Ruysch its celebrated discoverer.

The similitude which prevails between the mem-
brane thus formed by art, and certain remarkable
phenomena in diseases, especially in those of an
inflammatory nature, reduces it to a certainty,
that such phenomena are to be entirely referred
to the coagulation of the lymph, of which we are
now treating.

It may be proper on the present occasion to
mention a few of those numerous phenomena al-
luded to, which evidently derive their origin from
this property of the lymph; thus we may instance
in particular, the pleuritic crust, which is formed
on the surface of the crassamentum of blood re-
ceived into a vessel and suffered to remain some-
time at rest; the membrane-like appearances which
usually transude from, and completely invest the
surfaces of the several viscera when in a state
of inflammation; and also the membrana caduca
[Seite 16] of Hunter, which exsudes from the cavity of the
uterus, when impregnated, and still under the
gentle glow of the venereal orgasm. From the
same source originates likewise, that production of
cellular membrane by which we see frequently the
lungs connected to the pleura in cases of peripneu-
mony; as also the preternatural portions of the same
substance often found in the cavity of the abdomen
after profuse hemorrhages; and finally, to no other
source can we rationally refer those membrane-
like productions, which, in that singular species
of disease, vulgarly denominated Lithopoedion,
firmly attach to the contiguous viscera such parts
as are irritated to inflamation by the too long re-
tention of the calculus or stone in the abdominal
cavity. It seems to be also an opinion founded at
least on probability, that polypi, and such like
preternatural coagulated excrescences, owe their
existence to the same cause.

§ 20.

Those phenomena just enumerated, together
with a variety of others which every where occur,
demonstrate, in a most striking manner, the superior
importance of this lymphatic portion, in which
the vital principle of the blood appears immedi-
ately to reside, if indeed the blood possess any such
principle, an opinion which I think both ingeni-
ous and highly probable.

§ 21.

Besides those general portions of the blood al-
ready enumerated, we have on a former occasion
observed that this fluid contains also, in a state of
mixture, other elementary principles. (§ 10.)

What I principally advert to at present is air,
which is commonly believed to constitute 1/33 part
of the whole mass of blood, but which in the
blood of a living and healthy subject does not
exist in a free and perfectly elastic state, but is so
intimately united and involved, and so permanent-
ly fixed, as to be with difficulty extricated and
restored to its native aeriform state. Indeed I
have learned from actual experiments, that even a
very small quantity of the most pure air injected
through an artificial opening into the jugular vein
of a dog, has excited symptoms of a very formida-
ble nature, such as palpitations of the heart, drowsi-
ness, convulsions, and, when the quantity was slight-
ly increased, even death itself quickly succeeded.

§ 22.

The elementary parts of the blood thus concise-
ly treated of, differ very widely in the proportion
they bear to each other in different subjects, ac-
cording to the complex ratio of age, nourishment,
and other circumstances of importance, which re-
gard the sound health of each individual.

§ 23.

Neither has any thing more certain or decisive
been advanced with respect to the proportion which
the whole volume of blood bears to the entire
bulk of the body. Haller was of opinion, that in
an adult it amounts to 30 or 36 pounds by
weight; while the calculations of others have been
widely different.

§ 24.

The solids of the body are originally
derived from the fluids themselves; thus in the
first rudiments of the embryo, while yet in a gela-
tinous state, the solids, each in its own appropriate
situation, begin in a very gradual manner to as-
sume their proper form and texture, infinitely dif-
ferent from each other in point of cohesion, from
the most tender and almost pultaceous consistence,
such as the medullary substance of the brain, to
the most firm and durable, as the vitreous cortex,
or enamel of the teeth.

§ 25.

In all the solids of the body an earthy basis of
a calcareous nature abounds more or less, not in-
deed in a simple state, but united to the phos-
phoric and saccharine acids, the former of which
exists in by far the largest proportion. Their co-
hesion depends not only on the peculiarity of their
texture, but is also much promoted, as well by
the quantity of air contained in them in a fixed
state^*, (which is ascertained by the experiments
of the illustrious Hales to be more abundant as the
parts are more solid); as also by the substance
called animal glue, which is procured in large
quantities from the solid parts of animal bodies,
and is in general use in some of the mechanical arts.
The origin of this tenacious substance may be
very easily explained and comprehended from
what has been already said respecting the viscosity
or gluey nature of the blood.

The elementary substance of iron, to which has
been attributed the important office of increasing
the powers of cohesion in the different parts of
the human body, scarcely deserves to be taken
into consideration at all, as I have found its quan-
tity to be so very minute as not to exist in a
greater proportion than one fifth part of a grain
to two pounds even of the bones, the hardest and
most coherent parts of the animal system.

§ 26.

A great portion of the solids of our body very
evidently exhibits a fibrous texture, composed of
small filaments running more or less parallel to
each other. These filaments or fibres may be
evidently enough perceived in the bones, espe-
cially the bones of a foetus, in the muscular flesh,
in tendons, ligaments, aponeuroses, and some mem-
branes, as the dura mater, &c.

§ 27.

In various other parts of the animal body, the
texture is so widely different from that of which
we have just spoken, that in them it is scarcely
possible to trace the appearance of a single fibre;
their structure is indeed of a very singular and spe-
cific nature, distinguished in Greek by the name
parenchyma. This parenchymatous, substance is
almost exclusively confined to some of the secreting
[Seite 21] viscera of the system; thus it exists in the kidneys,
in the liver, &c. though assuming a somewhat dif-
ferent and peculiar appearance in each.

§ 28.

Through all those varieties of composition and
texture, whether of a fibrous or parenchymatous
appearance, there is interwoven, in common, more
or less of a certain web-like substance, which is
called cellular membrane, and which deserves a
place among the primary, the most important and
essential, constituent parts of our system.

§ 29.

For, in the first place, there are several of the
solid parts of the human body, which appear to
consist of little elsc than cellular membrane, in a
constipated or compacted state; of this description
are most of the membranes and cartilages; which,
by long maceration, may be again resolved into a
cellular web, of more or less laxity. It is, again,
so intimately and minutely interwoven in the com-
position of other parts, as to serve the important
purposes of a receptacle and basis to the other
portions of substance which assist in their formation.
Thus, for instance, the hardest bones made their
first appearance in the tenderer state of cartilage,
which, as already observed, is nothing more than
condensed cellular membrane: this cellular mem-
brane, yet in a lax condition, became afterwards
[Seite 22] distended, and at length completely saturated, as
it were, by the constant accession of osseous matter,
till it finally assumed the nature and appearance of
perfect bone. Indeed it would appear, that none
of the solids of our body exist, without containing
more or less of this web-like substance in their
composition, if we except the enamel of the teeth,
in which I was not able to discover the smallest por-
tion of cellular substance, even when the enamel
was subjected to the action of one of the stronger
acids.

§ 30.

This cellular substance, which serves the great
purpose of a boundary, or partition-wall, to adja-
cent parts, is especially interwoven in, as well as
spread between, muscles and membranes. To other
parts, again, particularly to vessels and nerves,
it answers as a bed or basis of support. Finally,
it constitutes one common and general bond of
union, which connects the neighbouring individual
parts to each other, and establishes between the
whole an extensive medium of communication.

§ 31.

From what has been already said, two conclu-
sions naturally present themselves.

First, in as much as it appears, that the cel-
lular membrane certainly constitutes the ground-
[Seite 23] work of the structure of the whole body, if we
figure to ourselves the entire removal of every
other substance which enters into, and assists in
completing, the composition of the system, the
cellular membrane, still remaining in its proper
situation, unmolested and alone, will nevertheless
preserve and exhibit the complete figure of the
whole and every part of the body.

Secondly, as by means of this cellular founda-
tion, a certain connection and medium of commu-
nication are formed, between all the parts of the
body, however widely different from each other
they may be, in nature, or remote, in situation;
the knowledge of this fact serves an important end,
not only in deciding controversies which respect
the continuation of membranes, but also in explain-
ing many phenomena of diseases which daily pre-
sent themselves.

§ 32.

As the cellular membrane appears thus to afford
origin and foundation to most of the solid parts of
the body, so it appears itself to owe its own exis-
tence to the lymphatic part of the blood, of which
we have already spoken. I am induced to enter-
tain this opinion from having seen the lymph, after
transuding from the lungs of pleuritic patients,
converted by the powers of the animal economy
[Seite 24] into real cellular substance, which afterwards
assuming the appearance of more compacted mem-
branes, oftentimes attaches those viscera to the
surrounding pleura.

§ 33.

What has been already advanced on the subject,
may be sufficient to show the general nature, and
establish the importance, of the cellular membrane.
We will now proceed to consider some of its
varieties.

And, in the first place, its firmness is not always
uniform.

For, in general, other circumstances being alike,
the cellular membrane of the human body is very
tender indeed, when compared with that of other
animals. If I am not deceived, this very softness
and pliancy of the cellular substance in the human
system, deserves to be ranked among the leading
prerogatives of man; because, in consequence of
it, his susceptibility of impressions from the more
refined and subtle stimuli is greatly increased, as
well as his capacity to perform motions and vari-
ous functions, with facility and perfection.

But with regard to the more lax or firm texture
of the cellular membrane, even among mankind
[Seite 25] themselves, a very great variety occurs, depend-
ing on age, sex, mode of life, climate, &c.

Finally, the condition of this membrane as to
density and firmness, is various, as it is found
existing in different parts of the same body: thus,
it is more lax on the eye-lids and prepuce, more
compact and firm about the ears, &c.

§ 34.

We now proceed to consider another use or
office of the cellular membrane, besides that
which we have already said it performs to the
body in general, (§ 29, 30); namely, that by
means of its numerous small cells, it affords con-
venient temporary receptacles for fluids of different
kinds.

That fluid, which those minute cells are more
particularly destined to receive, is a fine halitus of
a serous nature, or a very subtle water, by which
almost all parts of the body are moistened, and
lubricated, and which this cellular web appears to
absorb, after the manner of a sponge^*.

§ 35.

But, besides this, the cellular membrane, in
certain parts of the body, serves as a reservoir to
humours of a different and somewhat specific na-
ture. Thus, that portion of it which constitutes
the vitreous substance of the eye, is charged with
a fluid of the same name:

That which forms the meddullary membrane
of the bones (commonly, though improperly, cal-
led the internal periosteum) contains the medulla:
and,

Finally, A large portion interwoven through
the soft parts of the body, furnishes a convenient
receptacle for the other portions of oily substance.

§ 36.

And here indeed a threefold variety presents
itself to our consideration:

There are, in the first place, certain parts of
the body, the cellular substance of which, though
of a very soft and extremely flaccid nature, is
notwithstanding, never filled with fat in a healthy
subject; such, for instance is that which lines the
eyelids, and that spread on the genital organs of
the male, &c. But further, in numerous parts
throughout the body, there are not unfrequently
found irregular and transient collections of fat,
which appear to reside in the same kind of cells,
which at other times act as reservoirs to the atte-
nuated serous fluid already mentioned.

But finally, in certain parts of the body, and,
unless I am deceived, in cells of a peculiar nature,
and given description, fat is found constantly en-
closed, designed to subserve stated, uniform, and
specific uses in the animal economy, such, for ex-
ample, is that which, in the female system, forms
the mons veneris, which appears to me to consti-
tute a very peculiar and completely circumscribed
protuberance^*.

§ 37.

On the subject of the fat itself we will now pro-
ceed to make a few observations, this being so
very proper a place for entering on the considera-
tion of it.

It is an oil, not unlike the unctuous oils of ve-
getables; bland, inodorous, and lighter than
water, consisting of phlogiston, united to phlegm
by means of an acid of a peculiar nature.

§ 38.

It is formed at so late a period in the foetus,
that scarcely an indubitable vestage of it can be
discovered earlier than the fifth month after con-
ception.

Its consistence is various in different parts of
the body. That for instance which lines the in-
side of the orbit of the eye, is more fluid, whilst
that on the contrary which surrounds the kidneys
approaches to the firmness and appearance of suet.

§ 39.

A controversy has existed with respect to the
secretion of this substance, namely, whether it is
performed by a peculiar set of glandular bodies,
[Seite 29] agreeably to the opinion of William Hunter, or
whether it merely transudes, by simple diapedesis,
through the patulous mouths of arteries? The
latter of these opinions, besides other arguments
which might be advanced in its favour, appears
the most probable from hence, that not unfre-
quently preternatural collections of fat have been
discovered in other parts than those commonly oc-
cupied by this substance: this circumstance can be
much more aptly and rationally explained by at-
tributing such unusual collections of fat to an error-
loci, arising from a morbid state or disposition of
the vessels, than by referring it to an unnatural
and recently formed system of glands: thus for
example, in the very ball of the eye itself, fat has
been sometimes found; and a substance of a na-
ture like suet, usually fills up the cavity from
which a testicle has been extracted; indeed there
scarcely exists a cavity in the body in which stea-
tomatous collections have not made their appear-
ance.

But to conclude; those small glands to which
certain celebrated characters have been solicitous
to attribute the secretion of fat, appear as yet to
be in reality nothing more than mere creatures of
analogy.

But however this may be determined, it is in
the mean time very certain, that both the secre-
tion and absorption of this substance can be per-
formed with the utmost dispatch.

§ 40.

The uses of the fat are numerous. It lubri-
cates the solids, and thus facilitates motion. It
obviates and prevents a morbid excess of sensibi-
lity. It acts as a defence against cold: and,
finally, by its uniform distention of the skin, con-
tributes to comeliness and beauty. Not to men-
tion the peculiar uses of the fatty matter con-
stantly bestowed on certain parts of the body, as
the medulla of the bones, &c.

This substance appears, however, to contribute
scarcely any thing to the nourishment of the hu-
man species^*, when in the enjoyment of entire
health.

§ 41.

We enter now on the consideration of
a difficult subject, namely, the living solid, and
shall attempt a full account of the vital energies,
by which the different parts of our body appear
to be animated and fitted, as well to receive the
impulse of stimuli, as to perform the various mo-
tions which are necessary in the economy of the
living system.

§ 42.

But with respect to the living solid, it will first
be necessary to ascertain its exact limits, and to
define it with precision and accuracy; whence it
will evidently appear, that it is not our intention,
on the present occasion, to treat either of those
properties, which the human body possesses in
common with numerous other bodies in nature,
such as elasticity (the powers of which, however,
are notwithstanding exhibited in various motions
and functions of the animal economy), nor yet of
those which reside exclusively in the mind; tho’
we flatter ourselves no one will deny the powerful
influence of these latter over the energies possess-
[Seite 32] ed by the living solid itself, considered as a mate-
rial body. We will confine ourselves solely to
the consideration of those energies which reside in
our body as a system of organised matter, and
which appear to be related to each other in the
following order.

§ 43.

The first and most universal species of those vi-
tal energies, and which may indeed be regarded as
an inferior degree of the others, or rather as the
threshold leading to them, is simple contractility,
i.e. a propensity in a part to contract itself. As this
property appears in reality to reside in every part of
the cellular membrane, it must be equally exten-
five with that membrane itself, and therefore may
be said to pervade almost the whole body. Hence
this may be called, with perhaps sufficient propri-
ety, the vis cellulosa.

§ 44.

Another of the vital energies is, the irritability
of Haller, which resides in muscular fibres only,
and may therefore be called the vis muscularis.
It manifests itself by a very singular, oscillatory
and tremulous motion, easily distinguished from
simple contraction, by its being more readily ex-
cited to action on the application of any acrid sti-
mulus.

§ 45.

The third is sensibility, which resides solely in
the nervous medulla, communicating with the sen-
sorium, called therefore vis nervea; when any
part endowed with this property is acted on by
irritating stimuli, an impression is immediately
made on the sensorium.

§ 46.

The three foregoing may be, with propriety,
considered as common or general vital energies;
because they exist, more or less, in almost all, or
at least in a great many, parts of the body, which
the ancients called therefore similares, i.e. parts
of a similar nature.

§ 47.

But besides the foregoing, there exists also a
fourth energy worthy of our consideration, namely,
the vita propria, or specific life; under which deno-
mination I mean to arrange such powers as belong
to certain particular parts of the body, destined for
the performance of peculiar functions, and which
cannot with any propriety be referred to either of
the classes of common energies, formerly mentioned.

Inferring synthetically, or a priori, as it is
termed, it is not repugnant to sound induction to
conclude, that parts differing from all others in
[Seite 34] texture, in arrangement, and in peculiarity of
function, must also be furnished by nature with
peculiar properties and powers, adapted to the
performance of such specific action.

But reasoning analytically, or a posteriori, we
are likewise taught by accurate observations made
on nature herself, that there are certain parts of
the body, particularly some of the viscera, which
perform motions so very singular, as cannot by
any means be supposed to arise from either one or
other of the common energies, of which we have
already spoken, but must be referred to a vita
propria, or specific energies of their own.

Instances of such sigularity of action we have in
the motions of the iris; the erection of the papilla
in the breads of females; the motions of the fim-
briae of the fallopian tubes; the action of the
placenta; the action of the uterus in parturition;
the descent of the testes in the male foetus; and,
if I am not deceived, in a great part, if not in the
whole of the process of secretion.

§ 48.

The fifth and last energy which claims our at-
tention is, the nisus formativus, or formative pro-
pensity, which should be considered as the efficient
cause of the whole process of generation (taken in
[Seite 35] so extensive a latitude as to include both nutrition
and re-production as modifications of itself). In
consequence of this propensity, the matter of the
animal system, whether appropriated to generation
or nutrition, being lodged in the places destined
for its reception, and having acquired sufficient as-
similation and maturity, assumes forthwith its due
arrangement and figure, and enters into the com-
position of those parts which are afterwards fur-
nished and enlivened either with the whole or
part of the energies we have already enumerated,
viz. contractility, irritability, sensibility, or finally
specific life.

§ 49.

Of this nisus formativus, or formative propen-
sity, more will be said when we come to treat of
the process of generation.

Irritability will be more fully considered when
on the subject of muscular motion.

The subject of sensibility will be again resumed
when we come to consider the action of the ner-
vous system.

Of the vita propria, or specific life, we will
every where treat, when the subject under consi-
deration may render it proper.

But with respect to contractility, the present
is a very suitable place to offer on it a few addi-
tional and particular observations.

§ 50.

I have already said that this energy pervades
almost the whole body, at least, that its extent is
commensurate with the extent of the cellular
membrane.

In the first place, therefore, it resides in all
such parts as consist of compared cellular sub-
stance, of which the different membranes of the
body serve as examples. That these possess con-
tractility will not be denied by any one who re-
flects on the constriction of the dartos tunic, or
who calls to mind the spasms of the skin, or of
the peritoneum, which alone appears sometimes
to incarcerate and strangle the intestines in cases
of hernia.

Further, It also exists in such viscera as are
composed chiefly of this kind of membrane; of
this description are the lungs, the external super-
ficies of which is highly contractile, as I have
lately learned from frequently puncturing and irri-
tating them in a living state; but I have not found
them possessed of any real irritability, as has been
lately asserted by Varnier.

Even the bones themselves do not appear to be
entirely destitute of contractility, as we learn, not
only from the alveoli, which are well known to
become narrower after the extraction or loss of
the teeth, but also from the morbid affection term-
ed necrosis (i.e. mortification), from which it ap-
pears, that after a lifeless part of bone is quite re-
moved, the new production of bone, by which
the vitiated part was before surrounded, contracts
itself very gradually, almost to the natural thick-
ness and former figure of the part.

But as we observed on a former occasion,
that the vitreous substance of the teeth was quite
destitute of cellular membrane, so it appears to
me probable, that it is entirely destitute of con-
tractility also, because when a part of it is either
consumed by a caries, or broken off by accident,
the remaining portions or sides are not approxi-
mated to each other, as we have already said takes
place in the alveoli, but an irreparable hiatus or
chasm continues without a shadow of diminution.

§ 51.

This very power of contraction, possessed by the
cellular membrane, should be ranked among the
primary and leading securities or supports of firm-
ness and health; and to it should be referred that
tone of parts, so highly and favourably spoken of
[Seite 38] by the acute and ingenious Stahl. To advance
one argument in favour of the foregoing position,
from many which might be adduced, it is the cel-
lular substance which, in a healthy subject, ab-
sorbs, after the manner of a sponge the aqueous
liquid, of which we have already spoken, and by
means of its contractility propels it forward into
the lymphatic vessels: on the contrary, in a dis-
eased state, being deprived of its proper tone, and
reduced to an atonic condition, it becomes op-
pressed and distended with a load of water, and
thus gives rise to oedema and other cachectic
symptoms.

§ 52.

Finally, from the universal prevalence of con-
tractility throughout the whole body, we may
plainly infer its influence and contagious effect, as
it were, on the other vital energies; and also from
its infinitude of modifications and degrees in dif-
ferent men, we learn its highly influential part in
the constitution of both the proper health and pe-
culiar temperament of each individual.

§ 53.

Those three subjects (§ 1.) in the
consideration of which we have been hitherto en-
gaged, perpetually act and re-act on each other in
the living human body. The fluids, for example,
act by their stimulus on the solids; while these
again, in consequence of their vital energy, are
fitted and prepared both to receive the action of
the stimulating fluids, and to re-act on them in
turn. In a sound and healthy subject, this whole
routine of action and re-action, corresponds with
such exactness and definitude, as to constitute a
perfect and harmonious equilibrium.

§ 54.

There further exists in the living system a won-
derful consent of parts, even the most remote;
this consent is derived not from one, but seems to
owe its origin to different sources.

One of those sources resides in the nerves, de-
pending as well on the astonishing net-like anasto-
moses, formed by their numerous branches, as on
the intricate nature of their plexus and ganglia;
[Seite 40] by the medium of which, the impulse of stimuli
being communicated to the sensorium, may from
thence re-act on parts more remote.

Another source of this wonderful consent must
be referred to the different vessels of the system,
as well the sanguiferous as the lymphatic.

Another, again, arises from a certain similitude
of structure, giving origin to what may be called
a native sympathy.

The cellular membrane, which, as has been al-
ready observed, appears to constitute a common
bond of union to the whole body, may be readily
conceived to possess a very striking and powerful
influence in promoting the consent of distant parts.

§ 55.

Finally, to this head belongs what is justly es-
teemed one of the greatest mysteries of nature,
namely, the connection of the mind with the
body, and the diversified and astonishing power of
the one over the other. As this subject will be
again resumed, and treated more fully in another
place, it will be sufficient on the present occasion
briefly to observe, that besides the obvious power
of the will over most of the muscles, there are
also other faculties which exert their influence on
[Seite 41] the body, even without the concurrence or aid of
the will.

Of this description are those blind and purely
animal instincts of our nature; such, for example,
as that which excites to the gratification of vene-
real enjoyments.

Further, the body is greatly under the influence
of the internal senses, more especially of the ima-
gination, and those passions of the mind which it
contributes to excite.

Finally, it is by the interposition, and through
the medium of these, that a communication and
reciprocal influence are preserved between the
powers of the body, and the more exalted facul-
ties of the mind.

§ 56.

By this diversified consent of the solids, of the
fluids, and of the vital energies (§ 53.), by this
sympathy of parts (§ 54.), and by this intimate
connection between the mind and the body,
(§ 55.) life and health are preserved in vigour;
yet not always existing in the same, but in widely
different degrees of perfection and energy.

§ 57.

Between the two extremes of life there exist
different grades, of which one is called vita max-
ima, or perfect life; the other vita minima, or im-
perfect life.

Life is said to be perfect in the flower of age,
when the functions of the body have reached that
pinnacle of perfection, called by the Greeks acme;
this might also be denominated the athletic state.

Life, on the other hand, is said to be imperfect
when the functions are performed with less vi-
gour; although their perfection may be the most
consummate, when the situation of the subject, and
its mode of existence, are taken into considera-
tion: thus life is imperfect in a foetus in utero,
and that in proportion as the foetus is tender and
young. Finally, life is less perfect in the sleeping
than in the waking state; less perfect also in a
subject advanced in years, than in one basking in
the meridian blaze of manhood.

§ 58.

The varieties in point of health are no less nu-
merous and considerable: there is indeed a cer-
tain state of health which may be said to be pecu-
liar to each individual. Such persons as we sup-
[Seite 43] pose to be in the enjoyment of the most complete
health, differ, notwithstanding surprisingly from
each other, as well in consequence of a difference
in the constitution of the blood, as of a diversity
of tone, and of the other vital energies; hence
different individuals are so differently affected by
the same stimuli acting on their bodies. Perhaps
each individual may possess peculiar idiosyncra-
sies, though so very inconsiderable as to be scarce-
ly observable: the influence of custom is so pow-
erful, as to create, in different subjects, an intole-
rance of different impressions, though in them-
selves quite innocent; it also produces a facility of
bearing, and finally creates a desire for, such
things as appeared at first both unnatural and dis-
agreeable.

§ 59.

This appears to be the very hinge on which re-
volves the nature and variety of temperaments, so
frequently the subjects of physiological discusion.
The constitution of the temperaments depends, not
only on the proportion and mixture of the consti-
tuent parts of the blood (§ 22.), but also on the
peculiar vigour of the vital energies already treat-
ed of; and likewise on the consequent variety in
the mode of the reciprocal action and re-action of
the body and mind on each other. From this
combination and concurrence arises that peculia-
[Seite 44] rity of sensation to the impressions of stimuli; and
also that singular power of performing motions
with greater or less facility.

§ 60.

Hence the varieties of temperaments are lite-
rally infinite, and can never be reduced to any
certain and definite classes. But as it has been
the pleasure of physiologists to arrange them un-
der certain heads, for the sake of regularity, we
may with sufficient propriety give our assent to the
common mode of arrangement, by which they
have been reduced to four orders, namely, the
phlegmatic, the sanguineous, the choleric, and the
melancholic.

§ 61.

For although Galen erected this division on an
absurd foundation, falsely supposed to be derived
from the nature and constituent parts of the
blood, yet if this erroneous foundation be kept
entirely out of view, the division appears in other
respects so consonant to nature, that the different
temperaments of all men generally, and of every
individual in the different periods of life, may be
with propriety referred to one or other of these
four leading classes. Thus, in the tender age of
infancy the phlegmatic temperament chiefly pre-
vails. This in youth is exchanged for the san-
[Seite 45] guineous. The choleric marks the period of man-
hood. And the melancholic is the temperament
of old age.

But, as has been already observed, the variety
in the existing degrees of the same, and in the
mixtures of different temperaments, is so un-
bounded, as to afford an open and a very exten-
sive field of speculation to such as would wish to
amuse themselves with tracing out, and establish-
ing, on this subject, more minute combinations, or
divisions and orders.

§ 62.

This whole collective assemblage of all the fa-
culties and laws hitherto mentioned, by which the
functions of the human body are performed and
regulated from the opening, to the closing pulse
of life, are called human nature, or the nature of
man; from whence arose the name of physiology,
the science now under our immediate consideration.

§ 63.

Those functions of the body may be themselves
properly enough divided into four classes; which
division, although not entirely free from exception,
nor perfectly conformable to nature, may never-
theless be aptly enough retained as a useful assist-
ant to the memory.

I. The first class of this division embraces the
vital functions, so called because their incessant
and unmolested action, is more especially and es-
sentially necessary to the continuance of life. To
this class belong the circulation of the blood, and
after birth the process of respiration.

II. The second class embraces the animal func-
tions; these serve to distinguish animals from or-
ganised bodies belonging to the vegetable king-
dom^*. This class in man includes the connection
[Seite 47] of the mind with the body, but it regards more
especially sensation, and muscular motion.

III. The natural functions constitute the third
class. These are subservient to the nourishment
of the body.

IV. The fourth and last class consists of the ge-
nital functions, which are destined for, and employ-
ed in the propagation of the species.

Let us now consider each class of functions in
order, beginning with the vital.

§ 64.

The blood as we have already seen, af-
fords the primary origin to the principal parts of
the body, and continues afterwards to convey to
them uniform and perpetual supplies of nourish-
ment, and ought therefore, with a very few ex-
ceptions (§ 5.) to be distributed far and wide,
through even the most subtle and distant recesses
of the whole body. That such a minute distribu-
tion actually takes place, we learn not only from
a fine injection of the vessels, but also from every
day’s experience, from which it appears that very
[Seite 49] few parts of the body can be punctured with the
point of the smallest pin without the occurrence
of a greater or less hemorrhagy.

§ 65.

This vital liquid does not, as was the opinion
of the ancients, flow and ebb like the waves of
Euripus^*, through channels of the same nature
and order, but is so moved onward in an orbit,
or circulates, as they express it, in such a manner,
as to be carried from the heart, by means of the
arteries, to every part of the body; and being
there taken up by the veins, conveyed back again
by them to the same original fountain, the heart.

§ 66.

After a few, and those very indefinite, expres-
sions^† of his predecessors, William Harvey esta-
[Seite 50] blished, in a manner tolerably conclusive, the cir-
culation of the blood, in a small but immortal
work published in the year 1628.

In process of time, however, every shadow of
doubt on this subject was removed. This was
effected chiefly by frequent recourse to actual and
simple observations with the microscope; but in
part also by injections of wax and other substances
into the arteries, which were seen passing again
to the heart by the route of the veins; and, fur-
ther, by the elegant and sublime experiment of
[Seite 51] transfusing the blood of one living animal into
another, or into a human subject; as also by vari-
ous other experiments which may be performed
on animals in a living state.

§ 67.

What should be esteemed the definite standard
of the celerity of this motion, in a healthy human
subject, we are not well able to determine. In
this respect there is not only a difference between
one subject and another, but there also occurs a
great variety relating to this point, arising from
the difference of ages: there indeed exists a dif-
ference in the celerity of the blood’s motion, even
in the different parts of the same body.

Finally, the venous blood appears to glide on
more slowly than the arterial; and when flowing
through the trunks of vessels, its motion is more
rapid than when passing their smaller ramifica-
tions. Former physiologists, however, have not-
withstanding exaggerated these several diversities,
in the celerity of the blood’s motion, beyond their
natural magnitude.

The common conclusion, however, on this sub-
ject is, that the blood, flowing through the aorta
with its mean velocity, passes over a distance of
about eight inches during the space of one pulsa-
[Seite 52] tion; at which rate it would travel about fifty feet
in the first minute of time.

§ 68.

The globules of the cruor appear to revolve on
their axes or centres of motion; and it is said that
the same are propelled forward with greater velo-
city than the other constituent parts of the blood.
I know not whether this conclusion be drawn
from actual experiment, or whether it be only an
inference from an absurd application of the com-
mon laws of hydraulics to the circulation of the
blood: I call the application absurd, because it is
certainly the very summit of folly, to attempt to
account for that motion of a vital fluid, by which
it is carried through the living canals of an ani-
mated system, on the purely mechanical principles
by which water is forced through hydraulic ma-
chines. – As to myself, I must: acknowledge I have
never been so fortunate as to be favoured with
a view of this prerogative or precession of the
globules.

§ 69.

I am fully persuaded, that those globules only
glide forward, suspended or swimming in the fluid
formed by the other constituent parts of the blood,
but that they do not at the same time rotate on
their own axes at all. To conclude, it is not
[Seite 53] fully and clearly ascertained, that the blood, be-
sides its progressive motion, of which we are now
speaking, is also subjected to one of a different
kind, called an intestine motion; although there
can be no doubt, but that the elementary parts of
the blood may be occasionally affected in their
arrangement and combination, when they are
tumultuously agitated in consequence of the im-
mensely varied directions, the minute divisions and
numerous anastomoses of the vessels through which
they pass.

§ 70.

Thus much we thought proper to advance on
the motion of the blood in general. Previously
to our entering on a more close and minute con-
sideration of this subject, we think it best to treat
of the vessels in which the blood is contained, and
also to consider with attention the energies, by
which these vessels are animated, and fitted both
to receive and again propel the blood.

§ 71.

The vessels which receive the blood
immediately from the heart, and convey it to all
the different and minute parts of the body, are
called arteries.

In their collective or aggregate dimensions, they
are less capacious than the veins; but their texture
is far more solid, more compact, very elastic, and,
as appears, from the experiments of Wintringham,
remarkably strong.

§ 72.

They are composed of three membranous strata,
or coats.

I. Of an external, which Haller called a true
cellular coat, Albinus a nervous, Vesalius a carti-
laginous, others a tendinous, &c. It consists of
condensed cellular membrane, externally more lax,
but becoming by degrees more compact, as you
advance nearer to its internal surface, where it
is overspread with numerous small blood vessels.
[Seite 55] To this coat the artery appears to be chiefly in-
debted for its tone and elasticity.

II. The second or middle stratum, is composed
of transverse fibres, assuming a lunated or falciform
figure and direction; its substance has a fleshy ap-
pearance, from whence it has been called the
muscular coat, and in it the vital energy of the
arteries appears in a very particular manner, to
reside.

III. The last and most internal coat, is a mem-
brane of an extremely smooth and polished surface,
which serves as a lining to the cavity of the artery.

In the trunks and larger branches of the arte-
ries, these coats may be distinctly observed; but
they are less evident in the more minute ramifica-
tions.

§ 73.

All the arterial branches in the human body
take their origin from either one or the other of
two leading trunks.

The first of these trunks is the pulmonary artery,
which, rising from the anterior ventricle of the
heart, passes into the lungs.

The second is the aorta, which rises from the
posterior ventricle of the heart, and shoots its
ramifications into every part of the system.

These trunks are divided into branches, which
again undergo farther and more minute subdi-
visions.

§ 74.

An opinion has been conceived and propa-
gated as an established truth, that, throughout
the whole sanguiferous system, the aggregate capa-
city of all the branches, taken together, is superior
to that of the trunk from which such branches
directly originate. I fear, however, that the au-
thors of this opinion have expressed themselves
on this subject in terms by far too general, and
have sometimes even confounded the measure of
the diameter of vessels, with that of their area. In
my investigations and inquiries on this subject, I
did not trust to the result of a single experiment,
nor did I confine my experiments to vessels filled
with wax, which, however improper, were the
only kind used by some celebrated physiologists,
in their attempts to ascertain the matter now under
consideration; but, as the nature and importance
of the subject evidently demanded, I made my
experiments and observations on the sound and
unaltered vessels of subjects recently dead. I took,
[Seite 57] for example, that nameless trunk from which the
right carotid and subclavian arteries diverge as
branches, and also the brachial trunk, together
with its branches, the radial and cubital arteries,
and having formed a rectangular triangle, from
the diameter of the trunk and the diameters of its
appended ramifications, I found, from the well
known theorem of Pythagoras, that the square
of the hypothenuse was equal to the sum of the
squares of the base and perpendicular.

Indeed, in arteries of the smallest orders, Haller
himself acknowledged that the capacity of the
trunks is greater than that of their ramifications;
so that, at least, the common calculation does not
apply universally, but, (if it be indeed ever admis-
sible), must be restricted to a very few orders of
vessels.

§ 75.

Each trunk and ramification, separately consi-
dered, have been commonly believed to possess
a conical figure, the base, or that part next to
the heart, being supposed more capacious than
the opposite extremity. This opinion appears
however to be hypothetical: for, whoever will
take the trouble of examining the arteries with
accuracy and attention, will find their figure to be
perfectly cylindrical: indeed, on the other hand,
[Seite 58] there are not wanting instances of some arteries
which in their progress rather widen and expand,
such, for example, are the mammariae internae, or
internal mammaries, and even the arch of the
aorta itself is more contracted at its base than at
its apex or top. All arteries, especially those of
the larger orders, appear to be a little dilated and
enlarged, just before their division into branches.

§ 76.

The number of orders, formed by the divisions
of the main arterial trunk into the progressive
series of uniformly decreasing ramifications, from
its first origin at the heart, to its final termination
in the extreme capillaries, cannot possibly be uni-
versally ascertained and established as a general
and unvarying result. The truth of this position
will be obvious to any one who considers, that in
the different parts of the body, especially in the
viscera, the arteries are subject to great variety
with respect to their divisions; and that, on this
account, they sometimes form more, sometimes
fewer orders of vessels, previously to their sepa-
ration into evanescent capillaries.

Hence the disagreement of authors who have
attempted to amuse themselves with calculations
of this kind. Thus, for example, Keil estimated
the number of the orders of arteries at fifty, while
[Seite 59] Haller contended that they amount to no more
than twenty.

§ 77.

After numerous divisions of this kind, and va-
rious anastomoses, by which the neighbouring
branches of arteries communicate with each other,
they at length arrive at their final terminations,
which are completely continuous with, or which
fairly open into, the origins of veins; so that,
their route being uninterrupted, they are reflected
from extremities that can scarcely be discerned,
and thus converted into those returning vessels, by
which the blood, lately arterial, but now become
venous, is conveyed back again to the heart.

§ 78.

But although this complete continuity of the
arteries and veins be so extremely evident in nu-
merous parts of the body, as to be obvious even
to the naked eye, yet it still remains a matter of
doubt, whether this be the only and exclusive
mode, in which arteries communicate with veins,
or whether there may not be, at least in certain
parts of the system, an intermediate and parenchy-
matous substance, which receives the blood from
the terminations of the arteries, and again depo-
sits it in the incipient mouths of the veins?

There occur certain phenomena, such for ex-
ample, as erections of the penis, and the common
phenomenon of blushing, which render the ex-
istence of such a connecting medium between
those two kinds of vessels, at least not improbable.

§ 79.

There are, again, vessels of a nature evidently
different from those already spoken of, which ap-
pear to arise every where from the smaller arte-
rial branches; these vessels consist chiefly of two
kinds, namely, the serous, which are so narrow as
not to be able in a healthy subject to admit the
globules of the cruor, but only to receive the
thinner fluid or vehicle in which those globules
swim (§ 69.); and the secretory, which do not
appear to attract any thing from the mass of arte-
rial blood, but such specific fluids as are destined
for secretion (§ 4.)

§ 80.

With regard to the former kind of vessels,
which we denominated serous, it is necessary to
observe, that we do not mean by them the imagi-
nary orders of yellow and of white vessels, spoken
of by Boerhaave, which appear to have been fan-
cifully conceived, in conformity to the account
given by Leeuwenhoek of his equally imaginary
sixfold conformation of the globules of the blood:
[Seite 61] neither do we mean the neuro-lymphatic vessels
of Vieussen and Ferrein, of which those gentle-
men supposed the viscera to be in a great measure
composed; but which do not indeed appear to be
any better founded than the preceding conjectures
of Boerhaave and Leeuwenhoek.

By the serous we mean those colourless vessels
which are never visible, unless in certain cases of
violent inflammation, where the impetus of the
blood is very powerful; and indeed in some parts
of the body, even this energetic process of nature
is not of itself sufficiently powerful to bring them
into view, unless they be still farther dilated by
means of an anatomical syphon or injector: of this
latter description are, for example, the vessels of
the cornea, which can scarcely ever be filled with
wax, unless in the dead bodies of such subjects as
have died while labouring under a violent inflam-
mation of the eyes.

§ 81.

The secretory vessels, on the other hand, appear
to be different from those, and belong chiefly to
the secreting viscera and conglomerate glands;
they can also be traced by means of a very subtle
injection, which, for instance, when thrown with
force into the artery of the parotid gland, flows
out and escapes through the duct of Stenonius.
[Seite 62] But on these vessels we will have a stated oppor-
tunity of being more pointed and particular in a
subsequent section.

§ 82.

That blood, which, by means of the
arteries has been distributed throughout every
part of the system, must be conveyed back again
to the heart through the medium of the veins.

These vessels differ very widely from the arte-
ries, both in their functions and structure: to this,
however, veins of the smallest orders form an ex-
ception, as their structure does not differ from that
of arteries of the same magnitude in so wide and
obvious a degree.

§ 83.

The veins (if we except the pulmonary system)
are more capacious in their collective or aggregate
dimensions than the arteries; their ramifications
are also more numerous; they are much more ir-
regular in their courses and modes of ramifying;
[Seite 63] their texture is also much softer than that of the
arteries; they are far less elastic, but nevertheless
extremely tenacious, and capable of wonderful ex-
pansion.

§ 85.

Their coats are considerably thinner than those
of the arteries; whence the blood which they
contain appears in some measure through them;
they are also less numerous, being no more than
a certain cellular covering, somewhat resembling
what has been called the nervous coat of the ar-
teries, and an internal membrane of a very exqui-
site polish, similar to that with which the arteries
are lined.

No part of the venous system is furnished with
muscular fibres, except the larger trunks near the
heart.

§ 86.

In by far the greater number of the larger
veins, such, for example, as exceed in their dia-
meter the twelfth part of an inch, this internal
membrane forms, by its foldings, an immense num-
ber of valves of the most beautiful structure, ex-
ceedingly pliant or moveable, and exhibiting the
appearance of small sacks: they are, for the most
part, simple and alone, frequently however, ar-
[Seite 64] ranged in pairs, and sometimes in triplets; and
are so situated and disposed, that the bottom of
the little sack points to the origin of the vein,
while its mouth or orifice opens, and is directed
towards the heart.

Those small valves are, nevertheless, wanting in
the veins of certain parts, as in those of the ence-
phalon, the lungs, &c. and in the whole system of
the vena potarum.

§ 87.

The small ramifications of the veins (which
would, indeed, with more propriety be called their
radicles or little roots) form, by their junctions,
larger branches, and these unite finally into six
leading trunks; viz. the two venae cavae, one cal-
led the superior, the other the inferior, and the
four trunks of the pulmonary vein.

The vena portarum alone exhibits one pheno-
menon peculiar to itself. The trunk of that vein,
on entering the liver is, after the manner of an
artery, immediately divided into branches, the
extreme ramifications of which become, at length,
radicles to the inferior cava, and finally lose them-
selves in the bosom of that trunk.

§ 88.

We need not, on the present occasion, again
advert to the common, and by far too general,
opinion, that the areas of the branches are more
capacious than the area of the trunk from which
they rise, nor yet to that respecting the conical
figure of single vessels, as what was said on those
subjects, when treating of the arteries (§ 74, 75.),
will apply with sufficient precision to the veins.

There are also among the veins, a few examples
of vessels being more capacious at a more remote
distance from the heart; such, for instance, is the
vena poplitea, where it passes between the condyls
of the os femoris.

What has been already said, with regard to the
final terminations of the arteries (§ 77, 78, 80.),
may, by making such obvious and necessary
changes, as are adapted to the different nature
and circumstances of our subject, be fitly applied
to the origins of the veins.

§ 89.

There exists, as we have already had
occasion to observe (§ 65), a two-fold communi-
cation between the arteries and veins: one, for
instance, at the minute extremities of each kind of
vessels (§ 77); and the other at the heart, their
common fountain, in which the leading trunks of
the whole sanguiferous system meet.

§ 90.

The heart is, as it were, the first active organ
and moving spring of the whole human machine,
as it is by the perpetual and truly astonishing
energy of this body, that the most important vital
function, namely, the circulation of the blood, is
performed, from so early a date of our existence,
as the fourth week after conception, down to the
closing period of transient life.

§ 91.

This active organ, by its alternate dilatation
and contraction, first receives and again ejects the
blood in the following manner. Into the anterior
venous sinus, and its appendage, the anterior auri-
[Seite 67] cle of the heart, the blood is conveyed from the
whole body, by means of the two venae cavae, viz.
the superior and inferior, and likewise from the
substance of the heart itself, by means of the coro-
nary veins, the common orifice of which is fur-
nished with a valve of a peculiar structure; and
from this auricle, it is again conducted into the
corresponding ventricle of the same side.

§ 92.

From this anterior ventricle (formerly called
the right ventricle, in conformity to the situation
of the heart in brutes) the blood is thrown into
the lungs through the pulmonary artery, which
was called by the ancients vena arteriosa; from
thence, by the four pulmonary veins, called in
former times arteriae venosae, it is conducted into
a common sinus, formed by their conflux, and
thence again into the corresponding auricle; these
were once called the left, but are now more pro-
perly named the posterior, sinus and auricle.

§ 93.

From the posterior auricle it passes on to the
ventricle of the same side, from whence it is distri-
buted, by means of the aorta, through the whole
arterial system appropriated to the other parts of
the body, and by the coronary arteries, through
the substance of the heart itself.

§ 94.

The blood having passed from the extreme and
ultimate branches of the arterial, into the incipient
radicles of the venous system, re-enters the two
venae cavae, (while that from the coronary arteries
is also returned by veins of the same name), and
thus the whole collective volume resumes again,
and incessantly continues, the same circuitous route
already described.

§ 95.

This circular and regularly progressive motion
of the blood through the cavities of the heart, is
powerfully directed, and the regurgitations of that
fluid are completely prevented, by means of small
valves, which surround and serve as portals to the
principal avenues which lead to the heart. These
valves are situated on the margins, or extreme lips,
of the ventricles which are adjacent to, and look
towards, their corresponding sinuses, and also at
the mouths of the two great arterial canals leading
out of those ventricles.

§ 96.

Thus a small venous ring or tendon, which
forms a partition between the anterior sinus and
ventricle, descending into the cavity of the latter,
separates into three small valves of a tendinous
appearance, each one of which was formerly be-
lieved to divide again into three apices or points,
[Seite 69] from whence they received the name of valvulae
triglochines or tricuspides. These valves are con-
nected at their points to fleshy columns, common-
ly called musculi papillares.

§ 97.

In like manner another small ring of the same
kind, which constitutes a partition between the
posterior sinus and ventricle, is also divided into
two small valves, which, from a certain supposed
resemblance to a sacerdotal mitre, have been called
valvulae mitrales.

§ 98.

At the entrance into the pulmonary artery, as
also at the mouth of the aorta, are situated, in an
annular or circular position, three valves much
smaller indeed than those already described, but
of a very elegant and beautiful figure and appear-
ance, and furnished with fleshy fibres; these have
been called valvulae semilunares or sigmoides.

§ 99.

Now it evidently appears, that by means of
these different kinds of small valves, sufficient pro-
vision is made against the irregular, confused and
retrograde movement of the blood. They easily
yield, and afford a passage to the blood when ad-
vancing regularly forward in the established course
[Seite 70] of its circulation. But they prevent the regurgi-
tation of this fluid, by becoming, in consequence
of its refluent effort, fully expanded like the swell-
ing of a well-filled sail, and thus completely closing
the orifices round which they are arranged.

§ 100.

The valve of Eustachius which, in the foetal
state, is stretched like a curtain across the mouth
of the ascending cava, becomes after birth (sooner
or later in different subjects) so gradually oblite-
rated for the most part, as to be rendered wholly
unfit for the execution of its former functions;
neither indeed does the system stand any longer in
need of it, as a passage is now opened and prepa-
red for the blood through the lungs, and its re-
turn from those viscera prevented by the semilu-
nar valves already spoken of, and as each subse-
quent column of blood, pressing from behind, must
pursue the same route with that immediately pre-
ceding it. But as it does sometimes notwithstand-
ing happen, that the passage of the blood from
the right side of the heart into the lungs is by
some means obstructed, we then learn from the
preternatural pulsation observable in the superior
cava, that the blood is repelled in a retrograde di-
rection from the right sinus into the two adjoining
great venous trunks.

§ 101.

It is a point of controversy, whether or not the
semilunar valves suffer the ventricles to be perfect-
ly and completely evacuated, or whether they do
not rather by means of their expansion intercept
a part of the blood in its escape from those cavi-
ties, and thus force it to take in some measure a re-
trograde course.

Observations made on frogs, and even on the
minute heart of the nascent chick, prove that in
those animals the heart is indeed completely eva-
cuated; but whether or not the same thing takes
place in man himself, when in a sound state of
health, is not yet clearly ascertained; if, however,
it be admissible, in physiological discussions to spe-
culate and draw conclusions from the structure and
mechanism of those valves themselves, as they ap-
pear on the dissection of the heart, the contrary
opinion appears the most probable.

§ 102.

The texture of the heart is altogether singular,
and peculiar to that organ. It is indeed fleshy,
but remarkably close and compact, and widely dif-
ferent from the common constitution and appear-
ance of muscles.

It is composed of small bundles of fibres, more
or less oblique, frequently ramifying in a singular
manner, contorted and wound spirally in diversi-
fied and truly strange directions; these fibres lie
over, and rest on, each other in certain orders of
strata, they are intermingled and closely knit to-
gether in the septum which separates the two ven-
tricles, and are fastened and firmly connected at
the basis of those ventricles by four cartalaginous
rings or bands, which (according to the accurate
unravelling and developement of the whole fibrous
texture of the heart, lately executed by the inde-
fatigable and illustrious Wolff), appear to serve as
a stay and support to the fleshy structure of the
ventricles, and also to separate and distinguish it
from the fibres of the sinuses.

§ 103.

Those fleshy fibres are every where overspread
with an infinitude of small nervous ramifications
of extreme softness, but they are more particularly
supplied with such an immense apparatus of blood
vessels, arising from, and belonging to, the coro-
nary arteries and veins, that Ruysch has declared
in his writings, that the whole fabric of the heart
appears to be composed solely of sanguiferous
tubes.

§ 104.

By means of the foregoing structure (§ 90.
seq.) and texture (§ 101. seq.) the heart is fitted
for the performance of those perpetual and uni-
formly equable movements, which return in such
general order, that the preliminary appendices
and ventricles themselves, are alternately contrac-
ted and relaxed, or perform, in alternate times,
those motions, called in physiological language,
systole and diastole.

§ 105.

With such definitude do they preserve this har-
monious order in their routine of contraction and
dilatation, that as soon as the appendices contract
themselves, to propel the blood, returning from
the lungs and venae cavae, into the ventricles,
these latter are at the same instant relaxed and
fitted to receive the same advancing wave of
blood; but in the subsequeat and next moment,
when it is the point of time for the ventricles,
now recently filled, to contract and force the blood
into the two arterial trunks, the appendices are
again relaxed, and their mouths rendered patulous
for the purpose of drinking in a fresh tide of ve-
nous blood as it rolls on in its usual course.

§ 106.

This systole of the ventricles, which is supposed
to consume about one third part of the whole time
of the heart’s pulsation, is performed in such a
manner, that the exterior sides of those cavities
are approximated and contracted towards the in-
termediate septum which separates the right ven-
tricle from the left; which contraction, especially
if we attend to the conical figure of those cavities,
appears fully sufficient to evacuate them of their
contents.

But besides this approximation of the lateral
parts of the heart towards each other, the apex
of that organ is, during its systolic motion, con-
tracted towards, and brought nearer to its basis;
as has been frequently observed not only in the
inferior animals both of cold^*, and warm blood,
but even in man himself, while in a living state^†.

An argument seemingly in favour of a contrary
opinion has been derived from, and founded in,
vulgar experience, from which it appears that the
apex of the heart strikes, during its systolic mo-
tion, against the left mamma or breast, and seems
therefore to be rather elongated than contracted
and shortened; this apparently conclusive argu-
ment will however have no weight with one who
considers, that those sensible percussions or strokes
of the heart are to be attributed as well to the im-
petus of the venous blood rushing into the appen-
dices of that organ, as to that of the arterial blood
forcibly ejected from its ventricles; by both which
sources of propulsion the whole heart is carried
towards and impinged against that region of the
ribs.

§ 107.

The impetus, which is by this systolic contrac-
tion of the heart imparted to the blood, is com-
[Seite 76] municated to the arterial system, receiving the
blood, in such a manner, that every systole of the
heart may be plainly perceived in such arteries of
the other parts of the body as can be felt by the
touch, (of which description are all those that ex-
ceed in their diameters the sixth part of a line),
and likewise in such other arteries as can by any
means whatever have their pulsations rendered
obvious to the senses: this can be easily effected,
for example, in the internal ear or eye, in either
of which a singular kind of motion can be excited
and rendered sensible, which (as well as the same
kind of throbbing or pulsatory motion so percep-
tible in the other parts of the arterial system) is
called the diastole of the arteries: of this diastolic
motion we shall have an opportunity to speak on
a future occasion, at which time we will take up
the inquiry, whether or not it is to be attributed
solely to the action of the arteries themselves, or
derives its existence from some other source.

§ 108.

In whatever manner this point may be deter-
mined, one thing we learn from experience, the
surest guide to truth, viz. that in a healthy sub-
ject, what is called the pulse of the arteries, is
precisely synchronous with, and perfectly corres-
pondent to, the motions of the heart; and like-
wise in a morbid intermission of the pulse, the
[Seite 77] heart and arteries still harmonize in their action,
by ceasing from, and again commencing, motion
at precisely the same moments.

§ 109.

The frequency of the pulsations of the human
heart in a healthy state, is extremely different in
different subjects. This diversity arises principally
from diversity in point of age, but partially also
from other conditions of the system, which at any
and every period of life constitute the health pro-
per to each individual; so that it is not possible
to ascertain and establish, on this subject, any cer-
tain and definite rule. It may nevertheless be pro-
per to mention the general result of my observa-
tions (made in our own climate) on the frequency
of the pulse in the different periods of human life.

In the first days after birth I have generally
found the pulsations of the heart of the tender in-
fant, while sound asleep, amount to about 140 in
the space of a minute.

At the expiration of the first year, they amount
to 124 in a minute.

At the end of the second year to about 110.

At the end of the third year to about 96, &c.

At that period in which the first set of teeth,
usually called the milk-teeth, drop out, the pulsa-
tions of the heart amount to 86 in a minute.

At the age of puberty to about 80.

In the prime of life, or at the period of man-
hood, to about 75.

And to about 60 at the sixtieth year of human
life.

In subjects still farther advanced in years, I have
scarcely found two in whom the number of pulsa-
tions were the same, at the same period of old
age.

§ 110.

All other circumstances being alike, the pulsa-
tions of the heart are more frequent in females
than in males.

If proper and necessary allowance be made for
the habit of body, they are less frequent in men
uncommonly tall, than in such as are rather low.
This circumstance I have ascertained to be a truth
by comparative observations made on the pulses
of dwarfs, and giants or men remarkably large.

§ 111.

On the subject of those varieties in the pulse,
occasioned by extraneous circumstances, vulgarly
called non-naturals, it is necessary to observe, that
a cold climate produces a slow pulse; thus, for
instance, the heart of a Greenlander when in
perfect health, does not pulsate oftner than from
thirty to forty times in a minute.

But it is an observation as common as it is
true, that the pulse becomes more frequent after
the taking in of aliment, and after an emission of
semen. The same effect is also produced on the
pulse by a want of sleep, by bodily exercise, or
by passions of the mind.

§ 112.

The foregoing observations relate to the na-
tural or healthy pulse, in the consideration of
which it seems more consistent, and agreeable to
nature, to direct our views to the heart, as its ex-
clusive source, than to the arteries, on which
physiologists have usually fixed their attention
when engaged in the investigation of this subject.

In this incessant routine, the heart continues its
pulsations, down to the extreme glimmerings of
life’s perishable flame; and even then, all its parts
do not cease from action at the same moment,
[Seite 80] but it is the prerogative of the right ventricle
with its appendices, the right auricle and sinous,
survive the left ventricle, and its appendices.

This may be sufficiently illustrated in the fol-
lowing manner: After the last act of expiration,
the lungs now in a collapsed state, can no longer
admit the blood to flow through them in its cus-
tomary channel, while at the same time that wave
of blood which they have just returned to the left
side of the heart, is from thence forceably expel-
led through the aorta, and thus urges forward by
a vis a tergo the advancing column of venous
blood: from this combination and concurrence
of circumstances, the blood returning with preci-
pitation and impetuosity, rushes violently into the
appendices and ventricle on the right side of the
heart, in consequence of which the parietes of
those cavities are thrown into convulsive efforts,
and thus continue to be agitated, for some time,
after the left side of that organ is completely de-
prived of all vital motion.

§ 113.

From a knowledge of this fact. viz. that
during the last vital efforts of declining nature,
the blood is propelled into the cavities on the
right side of the heart, we deduce, with the ut-
most ease, the cause of that state of depletion in
[Seite 81] which the larger arteries are found after death.
To the same cause also Weiss, and after him the
illustrious Sabatier, were desirous of attributing
the superior size of the cavities on the right, to
that of those on the left, side of the heart, espe-
cially in the corpse of an adult subject.

§ 114.

The whole of this motion of the heart, which
has been the subject of the preceding observa-
tions, is to a very considerable degree limited and
directed by the pericardium, in which the heart
loosely hangs, and by which it is completely en-
closed as in the walls of a prison.

The pericardium is a membranous sac, consid-
erably capacious, and accommodated to the figure
of the heart which it encloses. It takes its origin
from the membranes constituting the mediastinum,
and although, from its fineness, it may appear some-
what tender, yet we learn from the experiments
of Wintringham, that it is so very tenacious and
firm, as far to exceed in strength all other mem-
branes of a similar nature in the human body.

That the pericardium is a part of the first
importance in the animal economy, we safely
infer from this single circumstance, namely, that
throughout all classes of animals possessing red
[Seite 82] blood, it is found as constantly and uniformly ex-
isting as the heart itself; and records do not fur-
nish more than one or two examples of the human
heart having been found completely destitute of a
pericardium. These singular examples of such an
unnatural state of the heart are recorded in the
writings of Dinkler.

§ 115.

The internal surface of the pericardium is kept
constantly humid by a dew-like serous effusion,
which appears to exhale from the small arteries
of the heart itself.

In like manner a fluid, of a similar nature, ap-
pears to transude into the very cavities of the
heart, and to moisten and lubricate their surround-
ing parietes or walls.

In either case the effusion during the healthy
state of the part is of a serous nature, and not ac-
companied by any real lymph, unless the heart be
labouring under inflammation; but when this or-
gan becomes the seat of an inflammatory affection,
then genuine lymph transudes, giving rise, on the
external superficies of the heart, to fine filaments
of a hair-like appearance, together with those
preternatural portions of cellular membrane,
which in such cases connect the heart to the
[Seite 83] pericardium, but on the interior surfaces of the
cavities themselves producing excrescences of a
truly polypous nature. (§ 19.)

§ 116.

Having thus completed the consid-
eration of the organs in which the blood is con-
tained, we now pass on to take a view of the
powers, by which those organs are qualified and
fully prepared to keep that vital fluid in motion.

Let us, in the first place, take an attentive and
accurate survey of those powers which reside in
the heart itself, and which ought, without doubt,
to be considered as by far the most active and es-
sential in the great business of circulation: we
will then proceed to consider what may be called
the secondary and assistant powers, which we will
also find of high importance in the animal econo-
my, from the concurrent and effective aid which
they afford to the action of the heart.

§ 117.

It will at first view appear obvious to even the
most superficial observer, that it is a matter of
Herculean difficulty indeed, either to ascertain by
accurate calculation the force of action exerted
by the heart, or to determine with precision the
quantity of blood thrown into the aorta by that
organ at each pulsation; neither will the specula-
tive physiologist find himself beset with difficulties
of less moment, when he attempts to ascertain and
establish with definitude, either the distance to
which each projected wave of blood is carried by
the impetus it receives from the heart alone, or
yet the celerity with which such wave rolls for-
ward; but he will be surrounded with difficulties,
still encreasing at each advancing step, in his at-
tempts to render a just statement and accurate ac-
count of all such obstacles as oppose, and thus
greatly diminish the effects of the force exerted
by the heart, in its action on the circulating mass
of fluids.

§ 118.

A certain estimation may nevertheless be formed
of the power of the heart, by collecting and com-
paring the most probable conjectures which have
appeared on the above points of physiological spe-
culation. Thus for instance, if we suppose the
whole mass of blood to amount at a mean rate to
[Seite 85] 33 pounds, i.e. 396 ounces (§ 23), and estimate
the number of pulsations at 75 in a minute, i.e.
4500 every hour (§ 109); and further, if we
adopt the opinion that at each systole the left ven-
tricle ejects two ounces of blood, it will then fol-
low, that during the course of every hour the
weight of the whole volume of blood makes 22 3/4
complete transitions through the heart. We may
also form a tolerable conception and estimation
of the impetus with which the circulating blood
is propelled from the left ventricle of the heart,
by observing with what astonishing violence, and
to what a considerable height, the blood spouts
from one of the larger arteries when wounded in
the neighbourhood of the heart. Thus, from
the wounded carotid of an adult subject, I have
seen the blood, during a few of the first contrac-
tions of the heart after the accident, mount in
jets to the height of at least five feet.

§ 119.

But when we institute an enquiry for the dis-
covery of those unfailing fountains or springs,
which supply the heart with a force so powerful,
and at the same time so uninterrupted and lasting,
that which first attracts our attention, as being
foremost both in point of time and importance is
its irritability, (§ 44). This vital energy, as has
been already evinced (§ 90), is much longer pos-
[Seite 86] sessed by the heart, than by any other muscular
part in the whole human body.

That the parietes, or walls themseves of the
cavities, are irritated and excited to contract by
reiterated impressions from the circulating waves
of blood, is manifest from a well known experiment
of the illustrious Haller. From this celebrated
experiment, of that indefatigable physiologist and
acute philosopher, it appears, that he could at
pleasure grant, either to the right or left side of
the heart, the prerogative of a more protracted
vital motion, (i.e. of longer life) accordingly as
he first deprived the one side or the other of its
peculiar stimulus, the blood^*.

§ 120.

When the proportional quantity of the blood
is well adjusted to the size of the containing vessels,
and its quality uncontaminated by any morbid
change, its action on the heart, and the re-action
of that organ again on the blood, proceed with
such an equable, regular and happy facility, that,
when in a state of rest, we are scarcely sensible of
the circulation of this vital fluid, which is the kind
and constant dispenser of life and vigour to every
part of our bodies.

But if the circulating volume of blood be either
too abundant, or preternaturally scanty, but espe-
cially if this vital fluid be contaminated by the
admixture of any foreign substance, as noxious
miasmata, air in an elastic state, or poisons in-
jected into the veins, &c. the heart, either roused
immediately into excessive action, or depressed to
the opposite extreme of prostration and debility,
continues no longer fit for the salutary discharge
of its important function, but falls into motions
convulsive, irregular, and very widely different
from the equable tenor of its healthy action. Fo-
reign substances of the same kind, as air blown
into the veins, &c. are also sometimes able to
rouse again, and excite to motion, the heart of an
animal recently dead.

§ 121.

It has been a point of controversy, even in very
modern times, whether this extreme irritability of
the heart be essentially inherent in its own sub-
stance, or if it be not rather adventitious, and de-
rived, as some celebrated characters would induce
the world to believe, from the mysterious influence
of the nerves? We will hereafter have a fit oppor-
tunity of declaring our sentiments respecting the
whole of this controversy, when we come to con-
sider the doctrine of muscular irritability, under
which head, this subject of inquiry most naturally
[Seite 88] falls. On the present occasion it may suffice to
observe, that I am daily more and more convinced,
that irritability is a species of vital energy altoge-
ther peculiar in its nature, belonging exclusively
to muscular fibres, and completely distinct from
the vis nervea (§ 34, 45.) But, on the other
hand, it is no less evident and incontrovertible,
that the nerves do also possess a very powerful in-
fluence and command over the action of the heart:
this we learn, as well from the peculiar habit and
appearance of the cardiac nerves, from their soft-
ness, their defect of covering, and their singular
disposition and arrangement, as from the astonish-
ing consent of the heart with by far the greater
number of the functions of the human body, even
with those of the most opposite nature. In testi-
mony of the reality of this consent, it may be
sufficient barely to mention, the sudden and tran-
sient sympathy which, even in a healthy subject,
exists between all the passions of the mind and
the heart, together with that, which, in a great
many species of disease, manifests itself between
this organ and the prima viae.

§ 122.

But, besides those vital energies of the heart,
it possesses also another power, arising out of its
mechanical structure, which appears to contribute
not a little towards carrying on the circulation of
[Seite 89] the blood. The cavities of this organ being
closely contracted, in the time of its systole, and
the blood by this means completely expelled, a
vacuum is thus produced, into which, on the prin-
ciples of the well known law of derivation, the
neighbouring blood must of necessity flow; for, as
the valves prevent the regurgitation of the wave
just ejected, it follows of course, that the cavities
of the heart must then drink in, and swallow down,
with rapidity, the blood advancing in the trunks
of the veins.

§ 123.

We proceed now to enquire, whether or not,
any of the other organs through which the blood
passes, besides the heart itself, are furnished with
powers contributary to the continuance of the
circulation of that fluid. Judging from first prin-
ciples, or a priori, as it is termed, we are led to
suspect that such powers do exist; for it appears
hardly probable, that the wisdom of nature has
entrusted so important a function, on which the
life of sanguiferous animals immediately depends,
to one organ only, the faults and defects of which
might, in such case, with too much facility, be
attended with fatal consequences. But, reasoning
a posteriori, as they term it, i.e. from actual ob-
servations, made on the animal economy, we are
furnished with numerous facts sufficient to establish,
[Seite 90] beyond a doubt, the existence of such powers,
which we may therefore term secondary powers,
and which are able, not only to aid the action of
the heart, but, in some cases, to compensate for
almost the complete absence of the influence of
that important organ. A striking instance of this
nature, is the continued motion of the blood, in
certain parts of the body, on which the power of
the heart can have but very little effect, if indeed
it can extend to them at all: this phenomenon is
observable, as well in the venous system of the
liver, as in the placenta of the uterus; not to
mention numerous instances of foetuses having
been born, without the smallest vestige of a heart.

§ 124.

Of these secondary powers, the first to be men-
tioned is, the functions of the arteries, the influ-
ence of which, in promoting and continuing the
circulation of the blood, appears to be, indeed,
very considerable; although the true principles
and mode of their action, on this fluid, have not
yet been fully developed and established.

Speaking in general terms, there exists a very
considerable resemblance between the arteries and
the heart itself: that the arteries, for example,
have a muscular coat, is a fact of the utmost pub-
licity (§ 72.)

That they also possess irritability, has been very
generally known, since the famous experiments of
the illustrious Verschuir.

And, further, as the aspect or disposition of the
cardiac nerves on the heart itself is truly singular,
thus also the larger branches of the arteries are,
here and there, surrounded with astonishing reti-
cular intertextures of soft nerves.

§ 125.

Finally, It is well known to every one that the
arteries pulsate, and that indeed with such vehe-
mence and force, that if we suffer one of our legs
to lie over the other knee, the pulsations of the
popliteal artery are sufficient to elevate in a sub-
sultory manner, the superincumbent leg not only
alone, but even with a very considerable weight
appended to it. Indeed for a long time past, both
a systolic contraction and diastolic relaxation have
been attributed to the arteries, which motions
have been said to correspond and harmonize with
the alternate contractions and dilatations of the
ventricles of the heart.

Though the truth of this last proposition is
generally believed to be established and confirmed
by the simple testimony of the senses themselves,
the subject is nevertheless still embarrassed with
[Seite 92] various doubts and difficulties: these difficulties
immediately rise to view, when it is asked,
whether this vibrating or pulsatory motion,
which is felt on examination by the finger, is to
be attributed to the inherent energy of the ar-
teries, or to the impulse of the heart; and
whether the whole motion of the arteries does
not depend solely on the impetus with which the
blood is projected into the aorta, and thus im-
pinges against the sides of that tube, and its rami-
fications?

Dissections of living animals have not been suf-
ficient to decide this controversy. For it some-
times happens that during the live-dissections of
warm blooded animals you may discover the lar-
ger arteries pulsating, while at other times again
they appear in a state of complete rest. In man
himself, while in the enjoyment of vitality, I had
once an occasional opportunity of observing the
neighbouring trunks of the aorta and pulmonary
artery, to be perfectly destitute of all motion;
but it should not be forgotten, that this phenome-
non appeared in a case of monstrous or preterna-
tural formation of the parts. There are also ar-
teries which we sometimes feel in a state of violent
pulsation, and which we nevertheless know, from
anatomy, are, in consequence of their situation,
almost immoveable; of this we have an example
[Seite 93] in the cerebral carotid, where it passes through
the canal of the os petrosum.

§ 126.

When all circumstances relative to this subject
are impartially weighed and dispassionately consi-
dered, this appears to be the result, viz. that the
diastole of the larger arteries takes place in conse-
quence of their peculiar nature, and is to be attri-
buted to the impetus of the blood rushing for-
cibly into them, and expanding their coats or tu-
nics, which, by means of their elasticity, imme-
diately return again to their natural dimensions.
To the same impulse also should be attributed
that lateral or curving motion of their axes,
which may frequently be observed in the larger
arteries when they run in a serpentine direction,
and lie embedded in soft cellular membrane.

But in a sound state of the system, we contend
that the arteries scarcely exhibit any unequivocal
proofs of a true systole, i.e. they do not by a ge-
nuine contraction recede from their natural, to
smaller dimensions, as long as the heart is adequate
to the due performance of its momentous func-
tion; but although it be certain, that the arteries
do not always, yet we acknowledge that they do
sometimes, exhibit and exercise a power of real
contraction: thus for instance, when the heart is
[Seite 94] deficient in its action in consequence of labouring
under either a morbid ossification, or some other
species of disease, it is probable that then the
duties of this important organ devolve on, and
are discharged by, the arteries, and that the
blood is thus kept in motion by the vital energy
of those animated tubes.

§ 127.

As it has been the decided opinion of several
celebrated physiologists, especially the famous
Whytt, that the powers of the heart cannot pos-
sibly extend their influence to blood-vessels of the
smallest order, as, for example, to the extreme
terminations of the arteries, and to the incipient
radicles of the veins; they have therefore attri-
buted the motion of the blood, in that part of the
system, to a certain oscillatory action of those mi-
nute vessels themselves, by the help of which their
contents are propelled forward: and this same vi-
bratory motion they have also applied, with a
great deal of ingenuity, to explain and demon-
strate the nature of inflammation, &c.

There are indeed a variety of phenomena, as
well physiological, which shall be mentioned when
on the subject of animal heat, as pathological, par-
ticularly observable in spasmodic affections, ac-
companied with fever, which seem to favour the
[Seite 95] existence of such a power of oscillatory motion,
although no such motion has ever been actually
observed, even with the assistance of glasses, in
the dissections of living animals.

§ 128.

It yet remains to enquire also after those assist-
ant powers, by which the other parts of the veins,
besides their radicles or incipient roots, are fitted
to complete finally the return of the blood to the
heart. It appears, indeed, at the first view of the
subject, that the veins possess and exert a much
smaller portion of the active vital energies than
the other parts of the sanguiferous system, because
the return of the vital fluid, contained in those
vessels, towards the heart, seems to be owing to
the impetus of the arterial blood urging it on by
a vis a tergo, as well as to the valvular structure
of the veins themselves, which effectually prevents
the blood from regurgitating. That these minute
valves are of the utmost importance in promoting
and continuing the regular and free circulation of
the blood, is satisfactorily demonstrated by the fre-
quent congestions and infarctions, which happen in
those veins that originate in the inferior parts of
the abdominal cavity, and which are entirely de-
stitute of such valves.

But there are nevertheless a variety of argu-
ments which render it probable, that the trunks
of the veins do possess, and actually exert, certain
degrees of the vital energies; as is well exempli-
fied in the veins of the liver, and of the uterine
placenta (§ 123.), &c.

It is also well known to every one, that the ex-
periments first instituted by the illustrious Ver-
schuir, are highly in favour of the existence of a
vital energy in the veins.

And, that the two leading and extreme venous
trunks have a stratum of a true muscular nature,
we have briefly hinted on a former occasion
(§ 84).

§ 129.

These are indeed the leading powers which are
active in promoting the circulation of the blood,
and which derive their origin from the very
structure of the vessels in which this fluid is con-
tained. I say nothing of the manner or degree in
which the motion of this vital liquid is influenced
by weight, attraction, or such other properties as
are possessed by all bodies in common.

I also pass over in silence the more remote and
inconsiderable aids, which, in a human subject after
[Seite 97] birth, are afforded to the circulation of the blood,
by the exercise of the other functions of the system,
such as respiration, muscular motion, &c.

§ 130.

The lungs, which are very intimately
connected with the heart, as well from the vicinity
of their situation, as from their uniform intercourse
in the performance of their important function,
are two viscera, large in the human subject after
birth, but of such specific lightness, as to float on
the surface of water. They consist of a paren-
chymatous substance, of a spungy texture, and
even exhibiting somewhat the appearance of foam,
yet still considerably tenacious and strong.

§ 131.

The lungs fill up the two cavities of the thorax,
and thus lie in perfect contact with the sacs of the
pleura, to which, as well as to the other parts
contained in the thorax, they apply and accom-
modate themselves with the utmost definitude and
exactness.

§ 132.

These viscera are appended to an air tube com-
monly called the aspera arteria, which, (besides
an internal membrane, lined with mucus, under
which is expanded a nervous intertexture of ex-
treme sensibility), consists also of a muscular coat,
which surrounds the nervous expansion, and on
the posterior side is easily distinguished at the ter-
minations of certain cartilaginous arches, which
assist in the formation of the tube, but are not uni-
form in their number.

§ 133.

After the aspera arteria has entered the thorax
it first forms, by bifurcation, the two trunks of
the bronchiae, which as they shoot still deeper and
deeper into the lobes and lobules of the lungs, pass
again, by reiterated divisions and subdivisions, into
branches and ramifications, uniformly decreasing
in size. During these progressive and multiplex
divisions into inferior orders, both the small carti-
laginous rings, and their muscular coat gradually
disappear, till the evanescent extremities of the
tubes finally terminate in those minute cells,
which constitute by far the greater and more im-
portant part of the substance of the lungs, as their
office is to receive, and again discharge the vivify-
ing aerial element, in the process of respiration.

§ 134.

Those small air cells do not appear to possess
uniformly, either the same figure or dimensions.
With respect to the former of these, (viz. their
figure), it is in general that of a polyhedron. The
latter, (i.e. their dimensions), as far as their super-
ficial extent is embraced in the consideration, can-
not without the utmost difficulty, be ascertained;
but, if we consider only their aggregate capacity,
this, in the lungs of an adult subject, whose inspi-
rations are full and strong, is sufficient to admit
and contain about 60 cubic inches of air. We do
not here speak of the immense size, to which the
lungs may be expanded by inflation, after the tho-
rax is opened, but only of the quantity and volume
of air which they do actually admit in the living
subject, when the process of respiration is per-
formed with ease and vigour.

§ 135.

These vesicles or cells, destined for the reception
of air, are every where surrounded and bound
together by that common, but extremely tender,
cellular membrane, which, as we have already
learned, constitutes a general vinculum or bond of
union to the whole body. But it is necessary to
distinguish clearly and accurately between the two
kinds of cells which exist in the pulmonic system.
I have seen the air cells so separate and distinct,
[Seite 100] in the lungs of a healthy human subject, that a per-
son’s breath, gently and cautiously blown through
a very minute and tender ramification of the bron-
chiae, would elevate only a single circumscribed
cluster of vessels or cells, and would neither pass
into the neighbouring cells of the same kind, nor
yet into the common cellular membrane, which is
every where interposed between those cells in-
tended for the reception of air. But, if the breath
be urged with considerable force, the air cells
will be lacerated, and such a communication form-
ed with the surrounding cellular membrane, as to
give free passage to the subtle elastic fluid, and
thus the whole and every part, of the pulmonary
lobe, will appear to be inflated.

§ 136.

This exceedingly tender cellular membrane,
which encloses and lies between the air vesicles of
the lungs, is every where interspersed with innu-
merable small ramifications of both kinds of pul-
monary vessels, viz. of the pulmonary artery, and
of the four pulmonary veins, the branches of
which accompany the branches of the bronchiae,
and afterwards, form in their course, by an im-
mense number of divisions and subsequent anasto-
moses, reticular intertextures, and expansions of ex-
treme fineness and subtilty. This truly astonishing
reticular tissue, running in all directions through
[Seite 101] the cellular membrane, so completely surrounds,
and closely embraces, the cells destined for the
reception of air, that the whole volume of blood,
which passes in an incessant round through the
pulmonic system, is separated from the air taken
in at each inspiration, by nothing else than mem-
branes so amazingly fine and subtle, as scarcely to
be equal in thickness, (according to the observa-
tions and calculations of Hales), to the one thou-
sandth part of an inch.

§ 137.

As we have already observed, that each indivi-
dual ramification of the bronchiae has appended to
it its own peculiar cluster of air vesicles (§ 135), so
likewise it appears, that to every individual vesicle
of each cluster is peculiarly appropriated its own
system of small blood vessels, the minute rami-
fications of which communicate very frequently
with one another, forming those surprising reticu-
lar tissues already spoken of, but scarcely appear to
anastomose, in any degree, with the small blood-
vessels of the adjacent clusters. That this is a
truth we are taught, if I am not deceived, as well
from microscopical observations made on the lungs
of living frogs and serpents, as from more minute
and successful injections of the lungs of human
subjects: the same thing is also further evidenced
by certain pathological phenomena which may be
[Seite 102] observed in vomicae, and other similar topical affec-
tions of the pulmonic system.

§ 138.

It is necessary to mention also, in the last place,
that singular and striking apparatus of lymphatic
vessels, which spreads and appears, in a more parti-
cular manner, on the external membrane by which
the lungs are invested. To this apparatus of ves-
sels belongs that numerous assemblage of lympha-
tic or conglobate glands, which, though of a quite
different and distinct order, are nevertheless com-
monly confounded, through mistake, with those
glands in their neighbourhood, which are called
bronchiales.

§ 139.

The thorax, in which the lungs are securely
enclosed, has for its foundation or skeleton, bones
and cartilages, arranged and disposed somewhat
like the walls or sides of a cave. Though this
bony cavity, taken together as an entire whole,
be to a considerable degree firm and steady, yet
most of its parts are so pliant and moveable, as to
be well adapted for the performance of those mo-
tions which the business of respiration requires.

This pliability, or facility of motion is particu-
larly observable in six pairs of the true ribs, which
[Seite 103] being placed beneath the superior and first pair,
are more moveable in proportion as their situation
is lower; or their aptitude for motion is com-
mensurate with the superior length of their bodies,
and cartilaginous appendices, which connect them
to the margins on each side of the sternum, by a
species of articulation called amphiarthrosis.

§ 140.

Between the edges of those ribs lie two strata
of intercostal muscles, the fibres of which assume
indeed and pursue different directions, but which,
nevertheless, co-operate in their action in pro-
ducing the same motion in the parts to which
they are attached.

Across the basis or inferior part of the whole
of this cavity the diaphragm is stretched, somewhat
in the form and direction of an arch. This is a
muscle worthy of particular attention, and, to use
the words of Haller, next in importance to the
heart itself; its parts appear to depend chiefly on
the phrenic nerve for their fitness to co-operate in
the function of respiration, as was long since de-
monstrated by the celebrated live-dissections of the
immortal Galen.

The diaphragm alternates for the most part, by
an antagonizing motion, with the muscles of the
abdomen, especially with the external and internal
oblique, and the transverse muscles.

§ 141.

The thorax thus formed and finished is, in the
living human subject after birth, alternately dilat-
ed at the time of each inspiration, and contracted
again to its former dimensions in every subsequent
act of expiration.

In inspiration, the enlargement of the tho-
racic cavity extends, in a more especial manner,
laterally and downwards, so that the bodies of
those ribs of which we have particularly spoken
(§ 139) are elevated, and their inferior margins
or edges turned in some degree outwards; while,
at the same time, the arch of the diaphragm is
somewhat depressed, and brought nearer to the
position of a plain, or level surface.

But as to what is boldly asserted of the sternum,
viz. that its inferior end is at the same time pro-
truded forward, this is a phenomenon which I
must confess, I have never been able to observe in
the tranquil and unmolested respiration of a healthy
person.

§ 142.

This alternate motion of the thorax, which in
a healthy subject is indeed performed spontane-
ously and without effort, is uniformly continued
from the moment of birth to the extinction of life,
for the following necessary and important pur-
poses, namely, that the lungs themselves may, by
a similar vicissitude of motion, be expanded for the
free admission and convenient reception of the air
we inspire, and again contracted in order that the
same may be forthwith expelled.

§ 143.

For man, together with all other warm blooded
animals, is prevented, by absolute necessity, from a
lengthy retention of the air which he inspires; he
is obliged, after a very short period to discharge it
again, and exchange it for a fresh supply of this
vital pabulum or food, as the air has been termed,
even from the most remote ages. It appears in-
deed from the most common observation, that the
air which is inspired and retained any time in the
lungs, however great may have been its original
purity, suffers, in a very short time, such remark-
able changes as affect it with the most obvious
contamination, and, unless it be speedily renewed,
render it wholly unfit to be any farther employed
in the important process of respiration.

§ 144.

Enquiries have been instituted for the purpose
of ascertaining the nature of those changes which
the air we inspire undergoes in our lungs. Such
changes certainly do not arise, as was formerly
believed, from the loss of any mysterious principle
of elasticity, which resides in the air, but are evi-
dently produced by a decomposition of its elemen-
tary parts. For the atmospheric air which we
breathe is truly an astonishing mixture of elemen-
tary substances, very widely different from each
other in their natures. Not to mention the va-
rious heterogenous matters which this necessary
fluid contains; such, for example, as the aerial
seeds of the smallest and most simple plants, the
odorous effluvia arising from numerous bodies,
volumes of dust, and a thousand other similar sub-
stances, which for the most part float in the at-
mosphere. Not to mention, I say, these hetero-
genous bodies at all, the air which we breathe
always contains aqueous exhalations in larger or
smaller quantities, and is also more or less charged
with the matters of electricity and magnetism.
But finally, though the whole of the foregoing
substances be left entirely out of view, yet even
then the air of our atmosphere does not consist of
one simple aeriform fluid, but is composed of de-
phlogisticated, phlogisticated, and fixed airs.

The proportion of those elementary matters,
especially of such as are organic, is varied ex-
tremely from diversity of places, and by the nature
of the bodies which exist in these places. It is in
the mean time, however, the common estimation,
that the air of our atmosphere consists of about
1/4th part of dephlogisticated, 11/16ths of phlogisti-
cated, and 1/0th of fixed air.

§ 145.

It appears, that at each inspiration, (in which
an adult subject, breathing in a quiet and tranquil
manner, draws in about 30 cubic inches of air,) a
fourth part of the dephlogisticated air is decom-
posed, and, in a great measure, exchanged for
pblogisticated and fixed airs; so that the expired
fluid, being received into a proper vessel, extin-
guishes flame or coals when immersed into it, pre-
cipitates lime from the water which suspends it,
and far exceeds atmospheric air in its specific gra-
vity, &c.

§ 146.

It is probable that the igneous parts of the de-
phlogisticated air, i.e. these parts suited to favour
the process of combustion, being set at liberty by
the decomposition which takes place in the lungs,
enters the arterial blood, and is thus distributed
throughout the whole body; while, on the other
[Seite 108] hand, the basis of fixed air is carried back, along
with the phlogisticated and venous blood, to the
right side of the heart, and thence (as the an-
cients were pleased to express themselves) ex-
creted through the lungs like soot.

The more florid dye of the arterial blood, the
more obscure colour of the venous, and the simili-
tude of colours imparted to both kinds of blood,
when exposed to the action of those species of air
now under our consideration (§ 16), are circum-
stances very much in favour of the preceding
opinions.

§ 147.

In a foetus which has never yet received vital
air into its own pulmonic system, there is in general
less difference between the arterial and venous
blood, than in an adult subject, in whom the pro-
cess of respiration has already taken place.

After the infant is born, the new sensation, ex-
cited by the contact of an unusual element, in an
animal which had hitherto led an aquatic life, and
the application of various other stimuli altogether
new, appear to afford us a happy clue for explain-
ing the new motions which at that period take
place in the body, more especially the dilatation
of the thorax and the first act of inspiration.

When the lungs are dilated by this first complete
act of inspiration, a new passage is thus opened
through them for the blood, so that this fluid is
ever after diverted from the umbilical vessels to
the thorax.

But when this inspired air is, by that decompo-
sition of its elementary parts, of which we have
already spoken, rendered both noxious and trou-
blesome to the lungs, I ascribe to the most simple
preservative efforts of nature, the immediately sub-
sequent motion, by which this poisonous mephitis
is exspired, and profitably exchanged for a fresh
supply of the fostering pabulum of life.

From all the foregoing circumstances, taken
collectively, (especially if we attend to the great
influence of respiration on the circulation of the
blood, as demonstrated by the well known experi-
ment of Hooke), we are furnished with a much
better explanation of the celebrated problem of
Harvey, than has yet been given by most of the
other reiterated labours of physiologists, who have
attempted to solve that difficulty.

§ 148.

The leading function of respiration
has been already the subject of our consideration.
We will speak, in another place, of the part which
this sublime process acts, in blending and intimately
uniting the chyle with the blood, and also of the
services which it renders, in a variety of ways, to
almost the whole class of natural functions, (§ 63.
112.) We now proceed to consider its other uses
in the animal economy.

The first object or phenomenon which attracts
our attention, in this investigation, is the Voice,
which belongs to the human subject after birth,
and evidently proceeds from the lungs, as was
long since very justly observed by Aristotle, who
said, that no animals are vocal, i.e. possess the
power of emitting sound, but such as breathe
through lungs. For, by the denomination of voice,
we properly designate that sound formed, by means
of the exspired air, in the larynx, which is a small
apparatus or machine of the most exquisite struc-
ture, placed on the top of the wind-pipe or aspera
[Seite 111] arteria, somewhat like a capital on the summit of
a column.

§ 149.

This small machine is composed of various car-
tilages joined together somewhat after the form of
a capsula or casket. These cartilages are furnished
with a great and truly admirable apparatus of mus-
cles, in consequence of which, not only the whole
are rendered fit for motion collectively, but some
of them are also enabled to move individually and
alone, according to the different variations about
to be produced in the voice.

§ 150.

That part which is more particularly engaged in
the immediate generation of the voice is the glottis,
a very narrow passage leading into the wind-pipe
from above, to which is prefixed, or applied as a
lid, a minute cartilage called the epiglottis. That
sound is produced by the air expelled from the
lungs, striking, in a proper direction and with due
force, against the edges of this strait passage, is a
matter too plain to admit of a doubt.

§ 151.

Controversies have existed on the subject of
those changes that take place in the glottis, by
which the modulations of the voice are produced,
[Seite 112] namely, Whether this cartilaginous part be alter-
nately expanded and contracted, as was the opi-
nion of Galen, and afterwards of Dodart? or,
Whether the variations of the voice do not rather
depend on the tension and relaxation of its liga-
ments, as was held by Ferrein?

The latter of those, therefore, compared the
primary organ of the voice to a violin, the former
to a flute – i.e. the one set of disputants conceived
it to emit sound on the principles of a corded, the
other on those of a wind, instrument of music.

From a faithful collection, and impartial consi-
deration, of all the arguments which have been
advanced on this contested point, we are of opi-
nion, that both kinds of changes do actually take
place in the glottis when employed in the emission
of sound; but we, nevertheless, believe, that the
principal and most important of those changes de-
pend on and arise from the tension of the liga-
ments, more especially of the thyreo-arytonoidei
inferiores (which appear to have been the vocal
cords of Ferrein.

§ 152.

That all this mobility of the glottis, of whatever
kind it may be, is influenced and wholly directed
by the numerous muscles which belong, and are
[Seite 113] attached, to the larynx, may be fully established
by the following beautiful experiment, viz. If the
recurrent or wandering nerves (as they are termed)
be either secured in light ligatures, or completely
cut asunder, the voice of the animals subjected to
such experiments, will be in the former case, ren-
dered extremely weak and low, and in the latter,
entirely destroyed.

§ 153.

The faculty of whistling belongs in common
both to the human species, and to small birds of
note. To qualify them for this, singing birds are
furnished with a bifurcated larynx at each extre-
mity of the aspera arteria. But though human
subjects be supplied with only one plain and simple
larynx, yet they learn to imitate those small ani-
mals, as appears to me, by a co-arction or pucker-
ing up of their lips.

§ 154.

But song, which is composed of speech and a
harmonious modulation of the voice, I would con-
sider as peculiar to man alone, and as constituting
the leading prerogative of his vocal organs. The
faculty of whistling is, as already observed, a part
of the birth-right of birds: a numerous train of
the feathered race, and sometimes even dogs them-
selves, have also been taught to pronounce a va-
[Seite 114] riety of words. But I doubt extremely indeed,
whether any brute animals have ever yet possessed
a faculty of true and genuine song; whereas, on
the other hand, I believe there scarcely exists a
a nation so barbarous, where song does not very
generally prevail.

§ 155.

Speech itself is a peculiar modification of the
voice, chiefly by the aid of the tongue, but par-
tially also by that of the lips, the teeth, the palate,
and by the further assistance of the nose, combined
into the formation of words.

Hence the difference between voice and speech
appears very obvious and plain: the first is evi-
dently formed in the larynx itself; whereas the
latter is effected by the singular mechanism of the
other organs already mentioned. It is but just
and proper, however, to observe, that this last
position is not capable of universal application, as
there are a few nations (of which the Sinensians
may serve as an example), among whom their al-
most homonymous^* words are distinguished only
by a varied modulation of the voice itself.

But further, voice belongs in common to brutes
as well as to man; it is possessed also by the new-
born babe, nor is it wholly denied to such unhap-
py infants as have passed their lives amidst the
haunts, and in the gloomy society, of wild beasts,
nor even to those that have been born without the
sense of hearing. But speech is not acquired till
after the cultivation and exercise of reason; it
constitutes, therefore, no less than that operation
of the mind itself, a characteristic privilege, and
distinctive prerogative between man and the rest
of the animal kingdom. To serve all the pur-
poses, and answer all the demands of brutes, that
instinct with which nature has beneficently supplied
them, is completely adequate; of this instinct,
however, man is destitute, as also of such other
aids and individual powers as might enable him to
preserve and sustain life by his own solitary exer-
tions; he is therefore kindly furnished with the
prerogatives of reason and speech, by means of
which, embracing the advantages, and discharg-
ing the duties, annexed to a social state, he is able
both to disclose his own wants, and relieve those
of his fellow creatures.

§ 156.

That truly admirable mechanism, by means of
which speech and the pronunciation of letters are
[Seite 116] effected, has, since the celebrated researches of
that paradoxical character, Franc. Mercur. Hel-
mont, been very much illustrated and explained
by further and later enquiries, especially those of
Jo. Wallis and Conr. Ammanus.

That division of the letters by Ammanus into
I. Vowels, II. Semivowels, and III. Consonants,
is, of all others, by far the most simple and na-
tural.

I. Vowels he again divides into simple, as a, e, i,
y, o, u, and mixed, as, ä, ö, ü.

II. Semivowels are themselves either nasals,
such as, m, n, ng, (i.e. n placed before g in the
German language); or Orals (otherwise called
Linguals) such as, r, l.

III. Finally, Consonants he divides, 1st, into the
Sibilantes or hissing (i.e. into those consonants the
pronunciation of which can be continued for an
indefinite length of time). These are h, g, ch, s,
sch, f, v, ph.

2dly, Explosive, as, k, q, d, t, b, p, and

3dly, Double (or Compound), such as, x, z.

§ 157.

Finally, It yet remains to mention certain other
modifications of the human voice, which usually
occur as symptoms, or signs of either particular
passions of the mind, or more violent affections of
the organs of respiration. The greater part of
these modifications of the voice, such for example,
as laughing and crying, appear to belong exclu-
sively to the human race.

§ 158.

Most of the modifications which immediately
follow, are connected together by such a powerful
kindred alliance, that one of them is not unfre-
quently observed to pass into another. It must be
also further observed, that the greater part of
them do not always assume and exhibit the same
uniform appearance, &c.

To speak, however, in general terms, in the
act of laughing, exspirations short, interrupted, and
in some measure broken, follow each other in
quick succession.

Crying produces deep inspirations, which sud-
denly alternate with lengthy exspirations fre-
quently interrupted and broken.

Sighing consists in a lengthy, full, and strong in-
spiration, and a subsequent slow exspiration, which
is not unfrequently accompanied with somewhat
of a groan.

Coughing is produced by quick and sonorous
exspirations succeeding a deep inspiration.

Sneezing is a more violent and somewhat con-
vulsive exspiration, which had been preceeded by
a short and forcible inspiration.

The Hickup on the other hand consists entirely
of a single inspiration, sonorous, extremely sudden,
and at the same time of a convulsive nature.

The present seems a very suitable occasion to
speak of the phenomenon of yawning, which con-
sists in a full, slow, and lengthy inspiration, suc-
ceeded again by a similar exspiration, while, at
the same time, the jaws are drawn so very widely
asunder, that the air which is received into the
expanded sauces can enter with ease the Eusta-
chean tubes. One thing peculiar to this pheno-
menon is, its being extremely contagious, i.e. it
very readily excites to imitation: the cause of this
is, without doubt, to be sought for in the remem-
brance of the agreeable sensatious produced at a
former time, by the languid operation of yawning.

§ 159.

It is worthy of observation, that man in
a living state, together with the other subjects be-
longing to the class Mammalia, as well as the whole
feathered race, are distinguished from the rest of
the animal kingdom by this peculiarity, that the
native heat of their bodies far exceeds, in degrees
of temperature, the usual heat of the medium or
element in which they live. With respect to man
himself, it is however to be remembered, that he
appears to be inferior, in the heat of his system,
to those other kinds of animals we have just men-
tioned. Thus, in our climate, the heat of the
human body generally stands at about the 96th
degree of Fahrenheit’s scale, whereas, in other
animals belonging to the class Mammalia, the vital
temperature very considerably exceeds this point,
while it ascends still higher in individuals of the
feathered tribes.

§ 160.

Indeed, the degree of native heat possessed by a
healthy person is so constant and uniform, that in
[Seite 120] general, (provided we make allowance for the
state of health peculiar to each individual), its
range will include but a very few degrees of the
thermometer, whether the subject be exposed to
the inclemencies of the most rigorous climate, or
placed beneath the fervors of a tropical sky. For
the opinion formerly delivered by Boerhaave, that
man has not a power of existing in a medium of
such a nature as exceeds in temperature the native
heat of his own body, has, since the famous ob-
servations of that illustrious traveller and former
governor of Georgia, H. Ellis, been refuted by a
great number of characters learned in the science
of physiology, and the reverse completely demon-
strated and established by experiments well adapted
to the nature of the subject. In this particular,
indeed, appears to consist one of the great prero-
gatives of man, that imprisoned and confined to
no one climate or zone of the earth, he is able to
pass his life in any section of the immense globe
we inhabit, and is free to fix his habitation either
beneath the rigors of Hudson’s stormy channel,
where the quicksilver passes spontaneously to a
state of complete congelation, amidst the tempests
of Nova Zembla, or in the bosom of those glaring
solar fires, which scorch the glowing shores of the
Senegal.

§ 161.

We proceed now to enquire into the origin and
source of that astonishing fire, which minutely
pervades our bodies, and uniformly supplies them
with their necessary degrees of warmth. To pass
in silence over the visionary conjectures of the
ancients on this subject, some of the moderns have
attempted to derive animal heat, with all its phe-
nomena, from the matter of electricity and the
nerves, others from the attrition generated by the
circulation of the blood, others from the recipro-
cal friction between the solid elementary parts of
living animals, while others, again, have embraced
and defended different opinions.

§ 162.

But all those hypotheses are embarrassed with
insurmountable difficulties, whereas, on the other
hand, the utmost simplicity, and an entire cor-
respondence to the phenomena of nature, combine
in recommending and confirming that doctrine, in
which the lungs are considered as the focus or fire-
place where animal heat is generated, and the de-
phlogisticated part of the air which we breathe,
as the fuel that supports the vital flame. That
justly celebrated character, Jo. Mayow, sketched
out, formerly, the leading traces and first great
outlines of this doctrine, which, in our times, has
been greatly improved, extended, and farther
[Seite 122] elucidated, by the labours of the illustrious Craw-
ford.

§ 163.

The whole drift and tenor of Crawford’s theory
obviously results in this, that respiration, no less
than combustion, belongs to such process as are
called phlogistic; in which the phlogiston residing
in, and constituting a part of, our bodies, is ex-
pelled by the accession of free or sensible heat,
(which ought to be carefully distinguished from
heat existing in a fixed or latent state.)

For phlogiston and the matter of heat are ele-
ments of such contrary and opposite natures, that
the greater quantity of the one our bodies at any
time contain, the less, at the same time, is their
proportion of the other; thus, fixed air, for ex-
ample, is not supposed to contain more than 1/67th
part of the quantity of the matter of heat, which
belongs to an equal weight of atmospheric air, &c.

But it appears, from experiments, that atmo-
spheric air has a stronger affinity to phlogiston
than to the matter of heat, so that it unites itself
with the greatest readiness to the former, while, at
the same time, it sets at liberty the latter, which
had been hitherto held in a fixed and latent state.

§ 164.

When we come to apply the foregoing posi-
tions and principles to the phenomena of respira-
tion, it appears highly probable, that animal heat
is generated by a process of a similar nature.

For, as we have already had occasion to ob-
serve, the air which we exspire differs, in a very
remarkable degree, from what we had immediately
before inspired; being deprived of its igneous
portion, or of that part fit for contributing to the
support of flame, it is returned highly impreg-
nated, on the contrary, with phlogiston and the
base of fixed air. (§ 146.)

§ 165.

It appears, therefore, extremely probable, that
the igneous portion of the air we breathe enters
those minute blood-vessels, which are every where
dispersed throughout the substance of the lungs,
and separated from the air-vesicles themselves by
nothing more than subtle partitions of the most
filmy texture (§ 136); that from the lungs it is
conveyed through the pulmonary veins to the
aorta, from whence it is again, by means of the
arterial system, distributed throughout every part
of the body.

During the whole course of this minute distri-
bution, more especially while in the extreme ra-
mifications of the vessels, it appears to be ex-
changed for phlogiston, which it every where
meets with in considerable quantities. This phlo-
gistic principle, being thus mixed with the blood,
and occupying the place just evacuated by the
matter of heat, is conveyed back, by means of the
venous system to the right side of the heart, and
from thence by the pulmonary artery, into the
lungs, where, agreeably to those laws of affinity
which we just now hinted at, it is immediately
received and taken up by the volume of air
recently inspired. In consequence of the accession
of this quantity of phlogiston, and its union with
the air contained in the lungs, a fresh portion of
the element of fire or heat is set at liberty, which
instantly enters the blood and is thus incessantly
distributed throughout the system in the manner
already described.

§ 166.

The truth of this theory is evidenced by those
diversities between arterial and venous blood, to
which we have every where adverted. It is
also farther evidenced by the difference between
the specific heat of arterial, and that of venous
blood; thus the specific heat of the blood con-
tained in the arteries is to that of the blood con-
[Seite 125] tained in the veins, as 11 1/2 to 10. Finally, as an
additional evidence of the same thing, we might
mention, in the last place, that oscillatory action
exerted by the smallest order of blood vessels,
which was the subject of our attention on a
former occasion.

§ 167.

For it seems altogether probable, that those
extremely minute ramifications of the sanguiferous
system, are parts of such utility and importance,
that in proportion as their action is stronger or
weaker, a correspondent increase or diminution
takes place in that exchange of the element of fire
for the matter of phlogiston, which goes constantly
forward in the body, and also in the heat of the
animal uniformly generated by such exchange.

Those memorable and striking phenomena, from
which it appears, that animal heat (if indeed the
matter be determined by a thermometer, and not
trusted to the fallacious test of sensation), remains
in general at very nearly the same precise point of
temperature, little augmented by the summer’s
blaze, little diminished by the winter’s blast; and
further, that on certain occasions the heat of our
bodies is even increased in consequence of an im-
mersion in cold water – Those phenomena, I say,
seem to demonstrate, and reduce it to a certainty,
[Seite 126] that according to the variations that take place in
the temperature of the medium in which we live,
corresponding diversities immediately follow in the
action of the smallest vascular ramifications of our
bodies. From this singularly accommodating
power, resident in the minute extremities of our
vascular system, it follows, that on being exposed
to cold (which appears to act by increasing their
tone), they are immediately enabled to exchange
a larger quantity of the principle of phlogiston for
the igneous pabulum, and thus generate a higher
degree of heat; whereas, on the other hand,
they are obliged to exchange a much smaller quan-
tity, as often as they are rendered inactive by be-
ing subjected to the influence of a relaxing and
debilitating medium.

§ 168.

So various, and extremely diversified,
are the functions of the cutis, with which the hu-
man body is invested, that an enumeration and
complete account of the whole of them can
scarcely be comprehended with propriety under
[Seite 127] one and the same head; they would appear to
be more fitly arranged for consideration, each one
under that class of actions to which, from its
nature it belongs.

For, in the first place, the cutis is the organ of
touch, of which we will speak when treating of
the animal functions.

It is again the medium or instrument of inhala-
tion, by which office it makes a part of the
absorbing system of lymphatics; this shall be a
subject of farther consideration, when we come
to take a view of the natural functions.

Finally, It is the laboratory or organ of perspi-
ration also. This function agrees in a great
variety of respects with the process of respiration,
and appears therefore to be introduced with
sufficient propriety as the subject of the present
section.

§ 169.

The cutis is said to consist of a threefold mem-
brane, or of a membrane composed of three
laminae. These laminae or layers are the corium
or true skin, lying on the interior side, the cuticula
or cuticle making the exterior covering, and the
reticulum (i.e. the rete mucosum), which is spread
[Seite 128] between the two laminae just mentioned. Of each
of these we will treat severally and in order.

§ 170.

The cuticle, or epidermis, forms, as just ob-
served, the external covering to the whole body:
It is thus, from its situation, exposed to a free ac-
cession of the air, the immediate contact of which
element, scarcely any other part of the body can
bear with impunity, even in a sound state, except
the enamel of the teeth, the tubes of respiration,
and the alimentary canal.

§ 171.

The texture of the epidermis is simple to the
utmost degree, being entirely destitute of vessels,
of nerves and of pores. This texture, though on
the whole scarcely organic, is nevertheless highly
singular and striking; notwithstanding its semipel-
lucid and tender appearance, its tenacity is yet so
very considerable as to resist effectually, for a
great length of time, not only maceration, but
various other modes of generating putrefaction.

§ 172.

The origin of this filmy expansion is as yet in-
volved in doubts and difficulties. It is in the
mean time, however, probable that it springs,
along with the small bulbs surrounding the roots
[Seite 129] of the hairs, from the corium or true skin expanded
beneath it: that this is the case, we are led to in-
fer, from the myriads of minute and extremely
tender fibrils, by which it and the skin are con-
nected together.

When by any means destroyed, it is re-pro-
duced again with greater facility, than any of the
other solid parts of the human body.

§ 173.

That this membranous lamina is of the utmost
importance in the economy of organized bodies,
is incontestibly evinced by its universal prevalence
throughout both the animal and vegetable king-
doms. It may be observed already formed even
in the tender embryo itself, at so early a period as
the third month after the time of conception.

§ 174.

Underneath the cuticle is expanded a thin mu-
cous membrane, which, from an opinion entertained
respecting it, by its celebrated discoverer, is called
reticulum Malpighianum.

This reticulum or subtle net-like expansion, ex-
hibits the habit and appearance of mucus, ex-
tremely easy of solution: it can scarcely in any
part, except in the scrotum of AEthiopians, be sepa-
[Seite 130] rated entire from both the cuticle and true skin,
and thus be procured in the form of a genuine and
complete membrane.

§ 175.

The part now under consideration, constitutes
the primary and principal seat of colour in the
human race. In all men the true skin is fair and
shining; the cuticle also is semipellucid and whitish
in all nations, except the inhabitants of AEthiopia,
in whom it is more duskish and obscure. But in
the human subject after birth, the colour of the
reticulum mucosum is varied, in correspondence to
the diversities of age, mode of life, climate, and
also in proportion as the constitution is more or
less sound.

Thus, for example, of the five varieties, into
which the human race appears to me, to be with
much propriety divided, the first has the reticu-
lum more or less whitish. This description in-
cludes, besides Europeans, those who inhabit the
west of Asia, and the north of Africa, together
with the natives of Greenland and Esquimaux.

2dly, In the second variety, which includes the
inhabitants of all the other parts of Asia, the reti-
culum somewhat tawny, inclining to an olive
cast.

3dly, In the third, which embraces the inhabi-
tants of AEthiopia, it is blackish.

4thly, In the fourth, which consists of the ab-
origines of America, it is to a certain degree cop-
per-coloured.

5thly, Finally, in the fifth, which comprehends
the inhabitants of all the South Sea islands, it is
more or less tawny or brown.

But all, and each one of those varieties of co-
lour, as well as all other varieties, by which man
differs from man, and nation from nation, appear
to be so intimately blended together, and are dis-
posed to run into each other with so much facility,
that it seems scarcely possible to establish any divi-
sions or classes of them, but such as are plainly
arbitrary.

§ 176.

The Corium or true skin itself, to which the
reticulum and epidermis serve as a covering, is a
membrane of a peculiar nature; it is porous, te-
nacious, capable of vast dilatation, varied in its de-
grees of thickness, consisting chiefly of condensed
cellular membrane, and extremely close and com-
pact on its external superficies; it is more lax on
the internal surface, which, (if you except a few
[Seite 132] regions or parts of the body) (§ 36.) contains, for
the most part, a certain quantity of common fat.

§ 177.

Besides nerves and absorbents, of which we will
speak particularly on a future occasion, the corium
or true skin is also plentifully supplied with innu-
merable small blood-vessels, which run on its exte-
rior surface, and, as we learn from a successful
injection, invest the same with reticular expansions
of the most close and subtile texture.

§ 178.

Over the same exterior surface is also inter-
spersed an immense assemblage of small sebaceous
follicles, which thoroughly anoint the whole cutis
with a very subtle and limpid oil, of such a nature
as not to be easily evaporated and dried up. This
fine fluid should neither be confounded with the
common sweat, nor yet with that fetid substance
which infests only some particular parts of the
body.

§ 179.

Finally, almost the whole of the true skin is
planted with hairs of various kinds. The most
numerous and abundant of these are very short
and tender, inclining more or less to the nature of
down; of hairs which fall under this description,
[Seite 133] scarcely any part of the body is destitute, except
the eye-lids, the male penis, the palms of the
hands, and the soles of the feet. But, on certain
parts of the body, the hairs, being destined for
particular uses, grow to much greater lengths;
examples of this we have in the hair of the head,
in the eye-brows, in the eye-lashes, the hairs in
the nostrils, the whiskers, the beard, together with
such hairs as grow in the arm-pits, and about the
anus and parts of generation.

§ 180.

In general, man is indeed less hairy than most
other animals belonging to the class mammalia.
A difference exists, however, in this respect, be-
tween the inhabitants of different countries. For,
to pass in silence over those nations who are in
the daily practice of plucking out, as well the
beard, as the hairs which appear on other parts
of the body, there are not wanting certain tribes,
who are naturally destitute of hair; of this descrip-
tion appear to be the Tungusae and the Buratae.
On the other hand, we are informed by travellers
of the highest reputation in point of veracity, that
the inhabitants of Nadigsda, one of the northern
Kurilikian islands, are remarkable for the unusual
quantities of hair with which their bodies are pro-
tected.

§ 181.

Neither are the varieties fewer, which are ex-
hibited by the hair, in regard to length, flexility,
curliness, and, more especially, in point of colour:
this last property depends, in general, on the power
of climate, on age, and other causes, which exert
their influence in perfect conformity to the esta-
blished laws of nature; but it sometimes also de-
pends on a morbid and misplaced temperament, as
appears to be the case in the white natives of
AEthiopia. The colour of the hair corresponds,
for the most part, to that of the eyes.

§ 182.

There is also a further peculiarity in the direc-
tion of the hairs, on certain parts of the body;
thus, for example, on the vertex or crown of the
head, they pursue a spiral direction; on the pubes,
they diverge and point upwards; on the posterior
side of the arm, they look, (as on the ape, and
contrary to their direction on the satyr), towards
the elbow, (that is, they point from the shoulder
downwards, and from the wrist upwards): of the
directions pursued by the eye-brows and eye-lashes,
it seems unnecessary to say any thing on the pre-
sent occasion.

§ 183.

The hairs originate from the interior surface of
the true skin, which contains a quantity of fat:
they are fixed with considerable firmness in each
of the small bulbs, which are composed of two in-
volucra; the external involucrum is vascular, and
oval; the internal is cylindrical, appears continu-
ous with the epidermis, and serves as an immedi-
ate covering to those elastic filaments of which
each individual hair is itself composed, and which
are from five to ten in number.

§ 184.

The hairs are always completely besmeared with
an oily halitus, and are almost incorruptible. They
appear to possess more of the nature of original
electrics (or of electra per se, as they are called),
than any of the other parts of the body. Their
nutrition is extremely simple and easy, as is also
their re-production after having fallen off, unless
the cutis itself be labouring under some morbid
affection.

§ 185.

Besides other important purposes which these
common integuments of the body serve, they are,
in a particular manner, to be reckoned among the
number of the excretory organs of the system; by
[Seite 136] their assistance, in this point of view, certain foreign
matters, which would from retention prove highly
noxious, are hourly eliminated and totally removed
from the general volume of our fluids.

The truth of the above position is fully demon-
strated and established, by the well-known circum-
stance of miasmata being completely removed from
the system, under the appearance of exanthemata
or eruptions; it is also proved by the odours of
garlic, musk, and other substances taken into the
body, passing by the skin; it is still further demon-
strated and confirmed by the process of sweating,
and by other phenomena of a similar nature.

§ 186.

But above all, those excretory passages convey
off a certain fluid, which is called the perspirable
matter of Sanctorius, in honour of that most acute
and ingenious philosopher, who instituted the first
series of rational inquiries for the express purpose
of ascertaining its utility and importance.

It is necessary, however, to observe, that under
this appellation, physiologists commonly designate
excrementitious matters, which, if not opposite, are
at least exceedingly different, in their natures, and
which ought, therefore, to be distinguished from
each other with the utmost accuracy and care; as
[Seite 137] the excretion of sweat, for instance, from the
genuine matter of perspiration.

The former (i.e. the sweaty excretion) is a
liquid of an aqueous nature, saltish to the taste,
and which scarcely ever issues spontaneously from
the healthy body when in a state of tranquility
and rest.

But the latter, (viz. the genuine matter of per-
spiration), of which alone we intend to treat on
the present occasion, is an aeriform fluid, perman-
ently elastic, and bearing a very striking resem-
blance to that which we exspire by the lungs.

§ 187.

Like that elastic fluid, it is highly charged with
the principle of phlogiston, like that, it precipitates
quick-lime from the water in which it was sus-
pended, and, like that, it is also unfit both for
contributing to the nourishment of flame, and also
for supporting the process of respiration, &c.

§ 188.

The quantity of this fluid that exhales from the
whole superficies of the body (which, in an adult
human subject of the middle size, amounts by
measurement to about fifteen square feet) can
scarcely be reduced to accurate calculation.

For, that the scales, which from the time of
Sanctorius have been made use of for ascertain-
ing the exact weight of the body, are not well cal-
culated for determining the precise quantity of this
elastic fluid, may be easily understood from what
we have just now said respecting the different sub-
stances which are eliminated from the system by
the skin, besides the true matter of perspiration.

It was long since discovered, that the nature
and quantity of perspiration vary extremely, not
only in different persons, but even in the same
persons, at different times. It seems at present,
however, to be a point too well ascertained to
admit of a doubt, that there does really exist,
with respect to the matter perspired, a national
variety and peculiarity; the truth of this we con-
fidently rest on what has been said, by authors of
the highest veracity, with regard to the singular
and specific odours which are transpired through
the skins of the Caribeans, of the Greenlanders,
of the AEthiopians, and also of the individuals be-
longing to other barbarous tribes.

§ 189.

On considering what has been said with respect
to the vascularity observable in the texture of the
skin (§ 177), and also with respect to the analogy
that exists between the matter of perspiration and
[Seite 139] the air we expire (§ 187); and further, on consider-
ing what has been advanced respecting the power
and influence of the smallest vascular ramifications,
in the generation of animal heat – to him, I say,
who carefully weighs and attentively considers all
these circumstances, it will appear extremely pro-
bable, that there exists a striking similitude indeed
between the action of the lungs in respiration, and
that of the skin in the process of perspiration. It
will appear that there exists between the cutis
and lungs a reciprocal consent; so that the one
may be supposed capable of assisting and some-
what relieving the other, and even of supplying
its place, at least to a certain degree, in case of
any accident or derangement.

§ 190.

In support of this opinion we can adduce the
concurrent testimonies of a variety of phenomena,
observable not only in a sound, but also in a
diseased, state of the system.

Some of these phenomena are, for example,
those leading points, in which the human foetus,
as well as that of the other animals belonging to
the class mammalia, differ from the incubated
chick, or the young of the feathered tribes, while
yet enclosed in the parietes of the egg.

A further evidence in favour of the same
opinion, is that singular coldness of certain parts
of the body, even in warm blooded animals, (as
in the noses of dogs, &c.) which appears to be
referred with sufficient propriety, to a less phlo-
gistic action of the small vessels, with which those
parts abound.

On the contrary, from an encreased action of
the minute vessels in certain parts of the body, we
explain, with the utmost fairness and facility, a
variety of morbid symptoms, such, for instance, as
that singular heat and flushing in the palms of the
hands, which occur so frequently, and are so
strikingly observable in patients labouring under
a hectic fever.

With regard to that vicarious action of which
we formerly spoke, and by which we said it ap-
peared probable, that the functions of the lungs
and cutis lend mutual aid and assistance to each
other; that such an action does unequivocally
exist, we derive some force of testimony from those
phenomena in pathology, where human subjects,
after birth, and even after advancing to an adult
age, having their lungs almost totally destroyed by
a consumption, or highly vitiated by some other
contamination, have nevertheless survived such
melancholy misfortunes, for a long time, and in
[Seite 141] some cases have even passed several years, during
the whole of which period they appeared to be
almost entirely deprived of the use and advantages
of respiration.

§ 191.

Finally, It does not appear improbable, but
that the interior surface of the alimentary canal,
may also, besides its other primary functions, be
perpetually engaged in the performance of a phlo-
gistic process, not unlike that conducted by the
skin and pulmonary system.

This canal or tube appears, indeed, to be the
only interior part of the body, except the lungs
themselves, to which the atmospheric air has free
access; but that the air has really free access to
the primae viae, or first passages, as they are called,
and that we swallow that elastic fluid in con-
siderable quantities, are matters, much too plain,
to stand in need of any proof.

Further, That the air which we swallow
undergoes a change very similar to the change
suffered by that taken by inspiration into the
lungs, is satisfactorily demonstrated by the nature
of the air contained in the whole alimentary canal.

Finally, To all those concurring circumstances
we may further add, that truly astonishing con-
geries of small blood vessels, spread in profusion
over the interior surface of the intestines, which
is commonly believed to be equal in extent to the
external superficies of the whole body.

§ 192.

We come now to treat of another
class of the functions of the human body, which
embraces what we denominated the animal func-
tions (§ 63): by means of these, an uninterrupted
commerce and intercourse are kept up between
the body and the various faculties of the mind.
They belong therefore exclusively, (as indeed the
name itself plainly imports,) to organised and ani-
mated bodies; but as they pervade the whole
animal kingdom more universally than the vital
functions, they appear to have an exceedingly just
and well founded claim to the epithet, animal.

§ 193.

The organs which are principally subservient to
the exercise of these functions are, the cerebrum,
the cerebellum, and their appendage the medulla
spinalis, together with the nerves that originate
from these three sources. The whole of these
organs may, with sufficient propriety, be ar-
ranged under two leading classes, namely, the Sen-
sorium and Nerves. The former of these em-
braces (if we except the nerves themselves, and
those parts which constitute their more immediate
origins) all the remainder of that whole system,
which forms, more particularly, the vinculum or
medium of connection, that exists between the
offices or functions of the nerves and our nobler
part, the faculties of the mind.

§ 194.

On this division is founded that beautiful obser-
vation of the illustrious Sommering, in which he
alledges, that the relative magnitude which the
two preceding classes of organs bear to one
another, corresponds so accurately with the fa-
culties of the mind, that the smaller and less bulky
the nerves of animals are, when compared to the
size of the other organs or parts which we have
comprehended under the denomination of Sen-
sorium, the more vigorous and active are the fa-
culties or their minds. In this respect he observes,
[Seite 144] that man may be said to possess the largest cere-
brum or brain, if its bulk be compared to the
small size of the nerves that originate and proceed
from it, but not if its weight be compared with
the relative weight of the whole body.

§ 195.

Besides the bony cranium or skull, in which the
cerebrum itself is enclosed, it is still farther invested
with three involucra or coverings; these are the
dura and pia matres, between which is expanded
the third, viz. the tunica arachnoidea.

§ 196.

The dura mater, which lines, as a periosteum,
the cavity of the encephalon, is lengthened out
into a variety of partitions or processes. By its
falciform process, which is the most prominent and
remarkable, it separates from each other, the two
hemispheres of the brain; while, by means of that
process called the tentorium, it forms a partition
between the cerebellum and the parts situated above
it, and thus, by giving support to the posterior
lobes of the brain, prevents them from making an
undue pressure on the subjacent cerebellum.

Further, the dura mater, by various duplicatures
or doublings of its own membrane, forms what
are called the venous sinuses, while it gives them at
[Seite 145] the same time firmness and support, and prevents
them from being unduly compressed. Through
these sinuses the blood of the encephalon, or parts
contained within the cranium, glides back towards
the heart: this blood is said, by physiologists, to
possess properties peculiar to itself, and appears,
from actual calculation, to be so considerable in
quantity as to amount, at least, to one tenth part
of the whole mass of blood contained in the human
body.

§ 197.

Next to the dura mater lies the tunica arachnoi-
dea, so called from its extreme tenderness and filmy
texture. It is destitute of blood-vessels, (§ 5.),
and does not, any more than the dura mater, enter
the various sulci or furrows, and receive the dif-
ferent eminences or ridges, which mark the sur-
face of the cerebrum, but only expands, with uni-
formity, over the whole volume of that important
viscus.

§ 198.

Very different from this is the state and situa-
tion of the internal involucrum or covering of the
brain, on which the ancients bestowed the name
of pia mater. This membrane every where ac-
companies the cortical part of the cerebrum so
closely, that the innumerable small blood-vessels,
[Seite 146] with which it is profusely supplied, enter, and
even perforate the cortex itself, with their infini-
tude of minute ramifications; hence, when the pia
mater is separated by force from the cerebrum, its
external surface presents a smooth and exquisitely
beautiful polish, while its internal surface, on the
contrary, is considerably villous, and resembles, not
a little, those delicate radicles by which the mosses
adhere to their native soil, or places of growth.

§ 199.

Both the cerebrum and cerebellum are compos-
ed of a variety of parts, different from each other
both in texture and figure, the uses of which have
been hitherto generally unknown: these parts are
particularly distinguished by the four ventricles, as
they are called, the communication between which
has been of late traced and developed, with the
utmost accuracy, by the illustrious Monro: of
these ventricles, the two anterior and the fourth
contain what are denominated the plexus choroidei,
the uses and functions of which are also involved,
as yet, in intricacy and doubt.

§ 200.

In all parts, of both the cerebrum and cerebel-
lum, there exist two kinds of substance, one of a
cineritious or ash-colour, which is called the corti-
cal part, although it does not always form the
[Seite 147] exterior stratum, the other white and shining, and
therefore called the medullary portion. Agree-
ably to the observations of the illustrious Som-
mering, there is interposed between the two fore-
going substances, still a third, of a colour border-
ing on white; this body is most conspicuously ob-
servable in the arbor vitae of the cerebellum, and
in the posterior lobes of the cerebrum.

§ 201.

The proportion, which the cineritious substance
bears to the medullary, decreases as life advances;
thus, in infants it is greater, in adults less. Almost
the whole of this cineritious substance, is com-
posed of an immense assemblage and contexture of
the smallest sized blood-vessels, together with vessels
of an order still inferior, even so minute as to be
incapable of admitting any thing except a white
or colourless fluid of the most exquisite tenuity,
(§ 79.): a small number of these vessels passes
into the medullary portion, which appears to con-
tain in its own composition, (besides these minute
vessels and a quantity of very tender cellular mem-
brane), a soft pultaceous parenchyma, in which
physiologists, even when armed and aided by the
most powerful glasses, have not yet been able to
discover any uniform and definite texture.

§ 202.

In the cerebrum is observable a perpetual but
very gentle motion, bearing such a relation and
exact correspondence to the process of respiration,
that while the lungs are collapsed, and their
volume diminished in the act of exspiration, the
cerebrum is slightly elevated, but immediately
subsides again, when the thorax is dilated by
means of a subsequent act of inspiration.

§ 203.

What has been called by physiologists the me-
dulla oblongata, terminates in the medulla spinalis,
which is contained in that flexible tube, formed
by the vertebrae of the spine or back, and is still
clothed in the same membranes which we have
already seen investing the cerebrum or brain itself:
further, as the brain, so likewise the spinal marrow,
is found to consist of two kinds of substance, with
this striking circumstantial difference, however,
that, in the latter, the cineritious or ash-coloured
substance forms the internal, whilst the shining or
medullary composes the external, part.

§ 204.

From each of the foregoing sources, namely,
the cerebrum and cerebellum, together with the
medulla spinalis, the nerves primarily derive their
origins. These are small ropes or cords, of a
[Seite 149] colour more or less whitish, differing likewise in
their degree of firmness), which are minutely
distributed throughout almost all the other soft
parts of the human body. This opinion of the
minute, and universal, distribution of the nerves
through every part of the human system, though
admissible as a general rule, is, however, subject
to certain well founded exceptions.

§ 205.

For it appears from an infinitude of experiments
made by the illustrious Haller, and other able
observers, that there are several of the partes
similares (or similar parts § 46) of our bodies, in
which, the knife, and powerfully armed eye of
the anatomist, have not been able to detect the
smallest vestige of nerves, and where neither sur-
gical observations nor live dissections, often re-
peated by the most dextrous hand, have succeeded
in discovering even the faintest phenomena of
sensibility.

In an enumeration of such parts, as appear to
be destitute of sensation and nerves, we must em-
brace, besides the naked cellular membrane, the
epidermis, the reticulum mucosum, the hairs, and
the nails.

We include further, the cartilages, and bones,
with their periostia and marrow.

To these must be added, the tendons, the aponeu-
roses, and ligaments; as also most of the broader
and more extensive membranes, such, for example,
as the dura mater and tunica arachnoidea; the
pleura, with the mediastinae and pericardium; the
peritoneum; the cornea, &c.

Under the same head we arrange most parts of
the absorbent system, but more especially the
thoracic duct.

Finally, This catalogue of such parts as neither
possess nerves, nor are endued with sensibility,
shall be closed, by the addition of the secundines,
and umbilical cord.

§ 206.

The primary or nascent origins of the nerves,
emerging from the sensorium itself, have, as yet,
eluded the most zealous researches of the subtle
knife and prying eye of the anatomist: it there-
fore still remains a matter of controversy and
doubt, whether the nerves on each side of the
body derive their origins from the corresponding,
or from the opposite side of the sensorium? Cer-
tain pathological phenomena appear indeed to fa-
[Seite 151] vour the latter of these opinions. It has been also
lately established by the illustrious Sommering that
a true decussation or crossing of the optic nerves
does actually exist.

§ 207.

A certain continuation of the pia mater accom-
panies the medullary part of the nerves in their
course, in such a manner, as to form for them a
vascular cortex, or covering, of extreme tender-
ness. No sooner, however, do these cords emerge
from the cerebrum, or the spinal marrow, than
they assume a very singular habit and appearance,
by which they may be readily distinguished from
almost all the other similar parts of the body.
This peculiarity of appearance is produced by
small plicae or folds, which they exhibit, running
in angular directions, more or less oblique. These
folds were formerly described by P.P. Molinel,
who compared them, not inconsistently with pro-
priety and fitness, to the rugae of the lumbricus,
or round worm, or to the small rings of the aspera
arteria.

§ 208.

The nerves, especially those of the single or
unpaired orders, such, for instance, as the inter-
costal and vagantes or wandering nerves, are
every where furnished with ganglia, i.e. small
[Seite 152] bulbs, of a texture considerably compact, and of
a cineritious colour, somewhat inclining to a pale
red: the functions and uses of these bodies in the
animal economy have not yet been satisfactorily
ascertained and demonstrated. We are, however,
in the mean time, most inclined to adopt the
opinion formerly entertained respecting these sub-
stances by the ingenious Zinn. That acute phy-
siologist believed the ganglia to consist entirely of
mazy complications and intertextures of minute
nervous filaments originating from different sources.
In consequence of this intricate and uninvestigated
texture of these bodies, he conjectured, that each
nervous filament, or thread proceeding from them,
participates, or contains in its composition, a part
of every filament that enters into their structure,
however numerous those filaments may be, or
however different the sources from which they
originate.

§ 209.

Neither does there appear to exist any very
material difference between the nature of ganglia,
as just described, and of what are called plexus
nervosi. These latter are also indebted, for their
existence and form, to a similar concurrence and
anastomosing intertexture of nerves that originate
from different sources. The composition of such
nervous filaments as ramify and proceed from these
[Seite 153] plexus nervosi, appears to be also perfectly analo-
gous to the composition of those, that originate
from the ganglia, of which we have already
spoken.

§ 210.

But as the nascent origins of the nerves, so like-
wise (with a few exceptions), the final termina-
tions of their extreme ramuli, or remote filamentary
branches, are as yet involved in the depth of ob-
scurity. For if we except those few nerves that
terminate in a kind of medullary expansion, as the
optic nerve in the retina, and the soft portion of
the seventh pair, in that pulpy zone, contained be-
tween the spiral laminae of the cochlea of the ear
– If, I say, we except these two nerves, the eva-
nescent filaments of such of the others as enter the
viscera, the muscles, the skin, &c. become so mi-
nutely blended with the real parenchyma of the
parts on which they are distributed, and gradually
assume such a pulpy consistence, that the eye of
the anatomist can no longer trace them through
their mazy courses.

§ 211.

We have thus seen, that of the sen-
sorium, and nerves so generally and minutely
distributed throughout most parts of the body, a
complete system is beautifully constituted, which,
during the continuance of life, serves as a medium
of communication and mutual intercourse between
the body and the mind.

§ 212.

Various circumstances and phenomena combine
in rendering it probable, that the mind is indeed
attached and closely connected to the brain itself.
That the brain is thus honoured and dignified in
its alliance is very powerfully and strikingly
evidenced, by most of the instruments of sensation
being situated in the very vicinity of that organ;
by the astonishing conformation of its various
parts, considered with regard to their figure and
structure; but more especially by the phenomena
attendant on its morbid affections.

§ 213.

With respect to that connection of which we
have just hinted, I would further observe, that
certain physiologists, wantonly sporting in the de-
lusive fields of imagination, have suffered them-
selves to be so far influenced by the form and
situation of particular parts of the encephalon,
that they have considered, and even endeavoured
to prove, sometimes one, sometimes another of
these parts, to be indeed the very seat, and royal
court, (as it were) of the mind. This honorary
and sublime privilege, of affording a sacred seat
to our nobler and immortal part, some meta-
physical physiologists have been solicitous to
bestow on the pineal gland^*, others on the
cerebellum, others on the corpus callosum^†, and
[Seite 156] others, again, on that part which has been deno-
minated pons Varolii.

§ 214.

We are not by any means to suppose, that the
whole energy of the nervous system depends on
the encephalon alone; it is also derived in part
from the spinal marrow, and even the nerves
themselves possess such a degree of inherent or
native energy, as is sufficient of itself to throw the
muscles into a state of convulsion. This native or
exclusive energy of the nerves, appears to be
principally supported and preserved by that vas-
cular cortex or covering of those organs, of which
we briefly spoke on a former occasion (§ 205).
It is, however, a truth which ought not to be for-
gotten, that this inherent power of the nerves
themselves is less, and that energy, on the con-
trary, which is derived immediately from the
encephalon, greater, in man, than in other
animals, especially such as are supplied with cold
blood.

§ 215.

The office of the nervous system appears, in a
particular manner, to be two-fold. First, by means
[Seite 157] of this system, other parts of the body, especially
such muscles as are subjected to the influence of
the will, are excited to motion; of this function,
however, we will treat more fully in another
place. But, secondly, the nerves are peculiarly
subservient to sensation; whatever sensible impres-
sions are made on the body, they, like active he-
ralds, convey and announce immediately to the
sensorium, and there give rise to perception.

§ 216.

Finally, the sensorium is evidently possessed of
the following very singular faculty or power, viz.
that, having received sensible impressions through
the medium and agency of certain nerves, it is
able to re-act again in its turn, not only on the
same nerves, but also on such as are completely
different. In testimony of the truth and authen-
ticity of this position, it will be sufficient to men-
tion the action of the retina, when affected by-
light, on the sensorium, and the re-action of this
latter, again, in either constricting or dilating the
iris.

§ 217.

It is principally from this last source, that we
are to derive and explain most of the effects of
the imagination, and passions of the mind, on
the human body: of these effects we will speak
[Seite 158] more fully on a future occasion. To the same
source, also, must we refer that extensive and
diversified consent of the nervous system, which
prevails throughout almost the whole body (§ 14.),
and the astonishing power and influence of the
same, over most of the other functions of the
animal economy.

§ 218.

That the phenomena which we have just men-
tioned, proceed from certain properties essential
to the nervous system, is a position, that appears,
from observation and experiment, to be founded
on the most indubitable evidence. But, to eluci-
date and explain the manner in which this system
acts, in the production of such phenomena, is,
indeed, a difficulty of the utmost magnitude.

§ 219.

When we view the subject in a general light,
the various opinions, which have at different times
been advanced on this contested point, may be all
referred to two leading classes: one of these
alleges the action of the nervous system, to de-
pend on a certain oscillatory motion; while the
other supposes it to be produced by the motion of
a peculiar fluid, respecting the nature of which
physiologists, again, hold different opinions. Thus,
while some believe this fluid to be animal spirits,
[Seite 159] contained in, and passing through, vessels, others
contend, that it is a certain modification of matter,
similar to fire, electricity, or the magnetic effluvia.

§ 220.

Although I am disposed to adopt neither of
the above opinions as my own, yet it is proper to
observe, that most of the arguments, by which the
advocates of either hypothesis have endeavoured to
invalidate the other, appear to me to be as crude
and inconclusive, as they ought to be subtle, inge-
nious and forcible. This observation applies, as
well to the arguments made use of to prove the
oscillations of the nerves, as to those advanced for
the purpose of establishing the existence of a ner-
vous fluid.

§ 221.

If, indeed, our views of the subject be not erro-
neous, the two foregoing opinions may, without
impropriety, be united, and thus a third one
formed, more plausible, at least, than either of
the originals, namely, that a certain nervous fluid
does actually exist, and that this fluid is also capa-
ble of motion, and of being thrown into oscillatory
vibrations, when subjected to the action and influ-
ence of stimuli.

§ 222.

Not to mention various other evidences, which
might be obviously deduced, from the different
phenomena of the nervous system, the structure of
the brain itself, which bears a striking resemblance
to that of certain secreting viscera, appears indeed
to be highly in favour of the existence of a nervous
fluid. It is surely a matter too obvious to admit
of controversy, that there is no more need of any
direst tubes and canals, for the distribution of
such a fluid through the nerves, than there is, for
the conveyance of a liquid through brown paper,
or any other filtre.

The nugatory calculations, respecting the asto-
nishing rapidity, with which the animal spirits have
been supposed to hurry through their nervous
canals, in all parts of the system, are subjects too
hypothetical and visionary to merit our time, or
command our attention.

§ 223.

That an oscillation of the nerves does indeed
exist, is a position, powerfully supported by a great
variety of very striking and pointed physiological
phenomena. This oscillation must not, however,
be supposed to bear any resemblance to the rude
vibrations of tense chords, but is such a subtle,
tremulous motion, as may be readily conceived to
[Seite 161] take place in the tender, pulpy substance of the
brain. That hearing is excited by an oscillation
of a liquid, has been reduced to satisfactory de-
monstration. That an oscillatory motion somewhat
similar takes place also, in the act of vision, is
(though we should not be willing to repose impli-
cit confidence in the opinions of Leon. Euler) a
position founded, at least, on strong probabilities.
That the action of the other senses depends also
on an oscillatory motion of a similar nature, is an
opinion, which was not only embraced by the
illustrious Newton^*, but has been since ably and
successfully defended in the writings of the saga-
cious Hartley. It is on the principle of the exis-
tence of such a motion, that this last mentioned
author, has first happily accounted for the associ-
ation of ideas, and then, by the aid of this, pro-
ceeded to explain, with the utmost ingenuity, most
of the functions performed by the different facul-
ties of the mind^†.

§ 224.

One office of the nerves, as we have
already had occasion to observe, consists in com-
municating to the sensorium, impressions made by
external objects. This they do through the me-
dium of the external senses, which officiate as
watchful centinels to the body, and diligent in-
structors to the mind.

These, therefore, shall constitute, at present, the
sole object of our consideration. For to arrange
among the senses, the stimulus or propensity which
animals feel to evacuate their faeces, the sensation
of hunger to which they are subjected, or other
internal calls of nature of a similar kind, would
be, as Haller formerly observed, an unnecessary
species of subtility and refinement.

§ 225.

It ought to be remembered, that no other class
of functions belonging to the animal economy, is
subjected to such an astonishing variety in different
individuals, as that of the external senses, which
[Seite 163] constitutes the subject of our present consideration.
This infinite diversity, which exists between these
senses in different individuals, is either natural or
acquired, and relates to their greater or less acu-
men or sharpness, their subtlety, or to the manner
in which they are affected by similar applications
of the same stimuli.

§ 226.

In giving an entire and complete account of
the external senses, it appears most proper to
begin with the touch, this being the one which
manifests itself at the earliest period in the human
subject after birth. The organ of the sense of
touch is expanded over the whole superficies of
the body, and is so constituted and formed as to
be affected by much the greatest number of the
properties of external objects.

§ 227.

For we are not only made sensible of certain
qualities of substances by means of the touch
alone, as of heat, hardness, weight, &c. but there
also exist other qualities, such, for instance, as
figure, distance, &c. of which we acquire, a much
more certain and accurate knowledge by the aid
of the touch, though it must be acknowledged
that these qualities are at the same time subject to
the cognizance of some of the rest of our senses.

§ 228.

The touch is less liable to deception than the
other senses; and is capable of becoming, by cul-
tivation and attention, so exquisitely perfect and
refined, as to be able to compensate, in a certain
degree, for any deficiency in its sister senses, more
especially in that of vision.

§ 229.

The organ of this sense is indeed the skin in
general, concerning the fabric and texture of
which we spoke formerly; but those parts that
are more immediately subservient to the touch,
are the papillae of the corium or cutis vera; these
papillae exhibit various figures in different parts of
the body; they are indeed, for the most part, ver-
rucose, in other places they are fungous, in others
filamentous or thread-like, &c. under all which ap-
pearances, the extremities of the cutaneous nerves
terminate after the manner of small pulpy pencils.

§ 230.

But by far the most important and distinguished
instruments of the touch are, in particular, the
hands, the skin of which is imprested with a great
number of striking peculiarities. Thus, for ex-
ample, the skin on the palms of the hands, and on
each side of the joints of the fingers, is sulcated
and completely destitute of hair, for the purpose of
[Seite 165] facilitating the folding or doubling up of those
parts. The extremities of the fingers, on their
internal, and of the toes, on their inferior, sur-
faces, are furrowed with slight and very elegant
grooves running in directions more or less spiral:
but the former, on the exterior, and the latter on
the superior, sides, of their terminations, are pro-
tected from injury by nails.

§ 231.

These scutiform nails are possessed only by man,
and a few other animals, (belonging to the class
mammalia), which are also furnished with hands,
and excel in the acuteness of their sense of touch.
These nails appear to be designed for the purpose
of making a gentle resistance to the pressure of
the fingers when examining substances, and thus
aiding their action.

The nails, though of a horny nature, must
nevertheless be considered, on the whole, as pro-
ductions or continuations of the epidermis: for
immediately under them lies the reticulum muco-
sum, which in AEthiopians is black; and finally,
beneath this again is expanded the corium or true
skin, which is firmly attached to the periostium of
the extreme phalanx of the fingers. Also these
constituent parts of the nails are striated in a lon-
gitudinal direction. At their posterior margins
[Seite 166] (which are distinguished by small semilunar seg-
ments, of a shining or somewhat brilliant ap-
pearance) they are securely fixed in a groove
formed by a reflection of the cutis, from whence
by a daily, but very moderate, increase, they are
gradually protruded forward, in such a manner, as
to be completely renovated in every term of about
six months.

§ 232.

Tastes are certain impressions made
on, and perceived by, the tongue, and also, in some
measure, by the adjoining cutaneous parts of the os
internum (i.e. the inside of the mouth); these parts
are, in particular, the medium palati, the fauces,
the cheeks, and even the lips themselves; with
respect, however, to the whole of these auxiliary
parts, it in proper to observe, that they have no
perception of any tastes except such as are acrid
or intensely bitter.

§ 233.

The principal instrument of taste is the tongue,
an organ capable of the utmost agility in motion,
very pliable, and exceedingly changeable in point
of form: it consists of a fleshy texture, which ex-
hibits a striking appearance, somewhat resembling
the texture of the heart.

§ 234.

It is invested with involucra or coverings, which
bear a similitude to the different strata of the cutis:
these are, the epithelion, which corresponds to the
cuticle, the reticulum Malpighianum, and lastly,
a papillary membrane, that differs but little in its
structure from the corium or true skin.

§ 235.

The principal difference consists in this, that
the epithelion, instead of a fine cutaneous oil, is
lubricated and moistened by mucus, which exsudes
from that imperceptible orifice, named after Mei-
bomius, and also from the rest of that glandular
expansion, discovered by Morgagni: another point
of difference is, the conformation of the papillae,
which are divided into the petiolated, the obtuse,
and the conical; of these, the former, being very
few in number, are placed in a lunated arrange-
ment, at the root of the tongue, while the others,
being of various sizes, are crouded promiscuously
[Seite 168] and without order, on the back of the tongue,
but more especially on its edges and tip, where
the sense of taste is most acute and exquisite.

§ 236.

To these papillae pass the extreme filaments of
the lingual branch of the fifth pair of nerves, by
the offices and aid of which it appears probable,
that the sense of taste is proximately generated and
preserved.

For the ninth pair of nerves, and also that
branch of the eighth, which is distributed through-
out the tongue, appear to be subservient to the
various motions performed by that organ in chew-
ing, swallowing, speaking, &c. rather than to its
function as the immediate instrument of taste.

§ 237.

That the tongue may exercise the sense of taste
in perfection, it is necessary for it to be kept in a
state of complete humidity; the substance to be
tasted should also be a liquid, and ought to abound
with salts in a state of solution: for if either the
tongue itself, or the substances applied to it be
dry, it may then indeed examine them by the
touch, which it generally, possesses in an exquisite
degree, but cannot with strictness and propriety
be said to taste them.

When the tongue discharges the office of
tasting with most perfection and acuteness, the
papillae, situated on its apex and edges, appear to
be brought into a state of genuine, though slight,
erection.

§ 238.

By means of the sense of smelling we
perceive impressions made by the odorous effluvia
of substances, which being inhaled in inspiration,
come in contact with that part, in particular, of
the Schneiderian membrane, which invests each
side of the septum narium, and lines the convex
surfaces of the concha.

§ 239.

For although the whole of the internal nares,
together with the adjoining sinuses, which open
into them, be lined with a humid membrane,
similar in appearance to the Schneiderian, it
nevertheless appears to be diversied in its nature
in different places.

That part of the membrane, which is situated
near the opening of the external nares themselves,
[Seite 170] bearing a stronger resemblance to the other parts
of the real cutis, is overspread with sebaceous fol-
licles, which are completely mantled in clusters of
hair.

But that part which lines the septum narium,
and conchae, is of a fungous nature, and abounds
with small muciferous cryptae or cells.

Finally, Those portions which invest the
parietes of the frontal, the sphenoidal, the eth-
moidal, and the maxillary sinuses, are by far the
most tender and delicate of all, and are completely
overspread with an infinitude of minute blood-
vessels, which constantly exhale from their ex-
tremities a subtle dew-like fluid of an aqueous
nature.

§ 240.

The principal, if not, indeed, the only use of
those sinuses appears, therefore, to be, to furnish
a watery liquid, of such a nature, as has been just
described, which being first conveyed into the
three passages or avenues of the nares, may be
from thence communicated to those adjacent parts,
which, we have already said, constitute the imme-
diate instruments of the sense of smelling. By
thus supplying, with a due degree of humidity,
the parts which proximately form the olfactory
[Seite 171] organs, those sinuses contribute, not a little, to
preserve the acuteness and perfection of this in-
teresting sense.

For the attainment of this end, such a wise pro-
vision is made by the very situation of those several
sinuses, that in whatever position the head be
suffered to rest, one or other of them may still
discharge and deposit a quantity of this subtle dew,
on the immediate seat of the sense of smelling.

§ 241.

The fungous part of the nasal membrane, of
which we have already spoken, and which con-
stitutes the proximate organ of smelling, besides,
the immense number of minute blood-vessels with
which it is overspread (and which are rendered in
a particular manner remarkable, by this circum-
stance, that there are no other vessels in the whole
body equally liable to spontaneous hemorrhages);
besides these small blood-vessels, I say, this part
of the membrane is also furnished with nerves,
especially from the first pair, and also from both
branches of the fifth pair: of these, the first pair
appears to be of itself solely subservient to the sense
of smelling; while the others supply the parts, to
which they are distributed, with branches for the
purposes of common sensation, such, for example,
as that which gives rise to sneezing, &c.

§ 242.

The extreme filaments of this first pair of nerves
are not, (as is the case in the organs of touch and
taste), lengthened out and rounded into papillary
elongations, but appear to deliquate, or melt down,
as it were, into the spongy and uniform paren-
chyma of the membrane in which they terminate.

§ 243.

In new-born infants, the chamber destined for
the immediate reception of odours is narrow, and
as yet extremely imperfect. The sinuses, of which
we have already spoken, have at this time scarcely
made their appearance: hence, infants do not ac-
quire the sense of smelling till a late period, as the
expansion and complete formation of their internal
nares are but gradually and very slowly accom-
plished. The larger those instruments become,
and the more accurately they are formed and
finished, the more exquisite will be the acuteness
and perfection of this sense.

§ 244.

Finally, it is a truth well worthy of being re-
membered, that there is scarcely another external
sense, which possesses such a powerful connection
with, and influence over, both the sensorium itself,
and the internal senses, as that of smelling.

There is none subject to such striking diosyn-
crasies; none better calculated either to produce,
to prevent, or to remove, paroxysms of fainting.

Neither is there any one susceptible of more
delicate and pleasing impressions; the smell is,
therefore, happily termed by Rousseau the sense
of the imagination.

Nor are there, lastly, any other species of sen-
sations that appear to excite so clear and vivid a
remembrance, as that which specific odours recal
to the memory.

§ 245.

Sound, which is excited by a tremu-
lous collision of elastic substances, and propagated
from sonorous bodies, through the medium of the
air, is at length perceived by the sense of hearing,
after having proceeded onward in the following
order: viz. it is first received by a shell-formed
cartilage denominated the external ear, over which
[Seite 174] a few of the human species possess a power of
voluntary motion: being collected and concen-
trated, as it were, by means of this concha or shell,
it passes immediately into the meatus auditorius,
which is thoroughly anointed and defended by a
very bitter and somewhat yellowish cerumen, or
wax-like substance: at the internal extremity of
this meatus auditorius it strikes against the mem-
brana tympani, which is situated in an oblique
position, is firmly attached to an annular groove
in the os temporis, and forms a complete partition
between this meatus auditorius, or passage for
sound, and the middle portion of the ear.

§ 246.

Behind this membrane, the middle portion of
the ear, denominated the cavity of the tympanum,
is so situated as to have its fundus or bottom
pointing upwards and inwards.

It contains three small bones, belonging to the
organ of hearing, the external of which, called
the malleus, is connected by its handle to the mem-
brane of the tympanum; from its spinous process,
which runs in a forward direction, a bulb or globe
is formed, (especially in an adult subject), with an
annular groove surrounding its base; this small
globular head rests on the body of the incus.

The incus itself is attached to the minute knob
or head of the stapes, by its longer process, which
extends nearly to the middle of the cavity of the
tympanum.

Finally, the stapes, resting its basis on the fenes-
tra ovalis, looks towards the vestibulum of the
labyrinth, into which, sound, having percussated
against the membrane of the tympanum, is propa-
gated by means of the connections of those three
osiccula or small bones.

§ 247.

The Eustachean tube, running from the interior
parts of the fauces, opens also into the cavity of
the tympanum; the inferior winding passage of
the cochlea enters likewise into the same cavity;
over the mouth or orifice of this passage, called
the fenestra rotunda, a fine membrane of a peculiar
nature is expanded. Physiologists have not yet
ascertained and demonstrated, in a clear and satis-
factory manner, the uses of either of those two last
mentioned parts.

§ 248.

Lastly, in the deep and hidden recesses of the
os petrosum lies the labyrinth, or internal portion of
the ear, which embraces again three several parts.

These are the vestibulum, which is situated in
the middle between the other two, and into which
open, besides the fenestra ovalis, both the five
mouths of the semicircular canals that run in a
backward direction, and also the superior winding
passage of the cochlea, which extends and lies
anteriorly.

§ 249.

The labyrinth itself contains a very subtle, lim-
pid water, which has been named after the illus-
trious Cotunnius, and which that celebrated phy-
siologist discovered to be absorbed by two very
minute canals: these small canals, called by Co-
tunnius, aqueducts, (and by Meckel diverticula),
arise, the one from the vestibulum itself, the other
from the inferior winding passage of the cochlea.

§ 250.

The soft portion of the seventh pair of nerves,
together with the hard, (which afterwards passes
through the aqueduct of Fallopius), having en-
tered the internal chamber of hearing, transmits
its medullary filaments through the perforated
bottom of that cavity. These filaments pass, in
part, to the vestibulum and semicircular canals,
but are distributed more especially over the base
of the cochlea, where their extremities are ar-
ranged in such a manner as to run between the
[Seite 177] laminae or plates of the septum of the cochlea,
exhibiting the appearance of a fine medullary
zone, beautifully ornamented with plexiform striae
or streaks.

§ 251.

The oscillatory tremor which we formerly traced
and followed up, even to the fenestra ovalis,
(§ 246.), is from thence propagated to the vesti-
bulum, where, finally, through the medium of the
subtle aqueous liquid already described (§ 249.),
it strikes and impresses the auditory nerves them-
selves, which are distributed with infinite art and
ingenuity throughout the mazy circumvolutions
of the labyrinth.

§ 252.

The impetus of sound, striking against the mem-
brane, and being propagated through the cavity
of the tympanum, is thought to be modified and
regulated, not only by the muscles of the malleus
and stapes, which appear, in their contraction and
relaxation to be subject to the influence of the
will, but also by the chorda tympani, which is
situated in the middle, between the handle of the
malleus and the longer leg of the incus.

§ 253.

Those rolling or versatile globes,
denominated eyes, are to be considered as the im-
mediate instruments of the sublime sense of vision.
They are fixed as if on footstalks, by their optic
nerves (respecting the decussation of which we
have already spoken, § 205.), in such a manner,
that their insertions are not directly opposite to
the centres of the cornea and iris, but are placed
behind the imaginary axes of the eyes, in situa-
tions somewhat nearer to the nose.

§ 254.

Each orb is composed of various tunics or coats,
which inclose humours of different densities, and
so extremely pellucid, that the rays of light,
having entered the pupil or window in the ante-
rior segment of the orb, can pass through, with-
out the least interruption, to its bottom or opposite
side.

§ 255.

The external involucrum of the globe of the eye
is called sclerotica, the anterior hiatus or chasm of
[Seite 179] which is closed up by the transparent cornea,
which is a lamellated membrane, more or less
convex, and projects in a slight degree forward,
like a segment of a smaller globe protruding out
of a larger.

§ 256.

Next to the sclerotica lies the tunica choroidea,
which abounds in blood-vessels, more especially
in verticose or circuitous veins: this coat is stained
on each side by a black pigment, which loosely
adheres to its concave surface after the manner,
and with the appearance, of mucus.

§ 257.

The choroides encloses, finally, the retina,
which is the most internal of the common tunics
embracing the visual orb. This coat consists en-
tirely of the medullary substance of the optic
nerve, which having perforated the sclerotica and
and choroidea, is expanded on the concave sur-
face of this last involucrum, and there arranged
with the utmost beauty and elegance of structure.

§ 258.

The anterior border of the tunica choroidea
terminates in a cellular ring, which is, denominated
orbiculus ciliaris, and by means of which the cho-
roides is more firmly attached to a corresponding
[Seite 180] groove or depression in the sclerotica. From this
cellular girdle or attachment, two other membranes
of different kinds, (namely, the iris and ciliary
processes), originate and diverge from each other,
like two expanded circles.

§ 259.

The iris (the posterior surface of which, being
overspread with a dark pigment, is denominated
uvea) is situated anteriorly, is gently convex on
the surface next the cornea, and is surrounded on
all sides by a humour of an aqueous nature. That
segment of the iris, which lies next the nose is
narrower, while that which looks towards the
temples is possessed of greater expansion. Its tex-
ture consists entirely of condensed cellular mem-
brane, without the smallest vestige of muscular
fibres; upon the whole, it appears to be in reality
a membrane sui generis, as was formerly well
observed by Zinn, and not by any means an ap-
pendage to the choroides. On its anterior surface
it is differently coloured in different individuals,
and while distended and animated with a plenitude
of life, it exhibits somewhat of a floccose ap-
pearance.

§ 260.

The blood-vessels of the iris run principally on
its anterior surface, and, in the foetus, are con-
[Seite 181] tinued into what is called the membrana pupillaris:
respecting the nature and use of this membrane, I
have spoken more fully in another place^*. It
appears to be intended for the purpose of pre-
serving the iris, (during the rapid growth of the
ball of the eye), in a state of expansion, and thus
rendering it more fit for future motion.

About the seventh or eighth month of preg-
nancy, when the ball of the eye has now acquired
a considerable magnitude, this membrane begins
to open and give way in its centre; the elliptical
arches of its vessels are retracted in a very gradual
manner, and thus form, in my opinion, the small
interior ring of the iris; it is, at least, certain, that
not a single trait of this ring can be discovered in
the eyes of a foetus previously to the above-men-
tioned period.

§ 261.

The posterior of those two orbicular membranes,
of which we have already spoken, (§ 258) is
called the ciliary body or band; it runs in a back-
ward direction, and therefore, in its progress,
diverges still farther from the iris; by its external
border, which is gross and firm, it is attached to
the orbiculis ciliaris (§ 258), but by its internal,
[Seite 182] which is more fine and delicate, it embraces the
margin of the capsule of the lens: it is also shaded
with that same dusky pigment, of which we have
twice already spoken.

Its anterior surface, lying opposed to the uvea,
is somewhat striated.

Its posterior surface, resting on the vitreous
substance, is distinguished by about seventy plicae
or folds, which exhibit an extremely elegant
floccose appearance; these are called ciliary pro-
cesses, and are remarkable for a vascular apparatus
of inexpressible subtlety and beauty.

§ 262.

In the eye-ball itself, the membranes of which
we have been hitherto describing, there are en-
closed, in particular, three different humours.

The vitreous humour occupies and fills the
posterior, and by far, the greatest, portion of the
visual orb. It is distributed, in a countless number
of minute drops, throughout as many minute cells
of the membrana hyaloidea, in such a manner, that
the whole mass, consisting, in part, of membrane,
and in part, of lymph, exhibits the appearance of
a peculiar, tremulous jelly.

§ 263.

The anterior part of this vitreous substance,
has appended to itself, and embraces, in the ciliary
girdle, a capsule, in which is contained the chrys-
taline lens, surrounded on all sides by a very
subtle water, first discovered and described by
Morgagni.

This lens itself, is also composed of extremely
pellucid cellular membrane; it is by far more
dense than the vitreous substance, and is furnished
with so minute a quantity of genuine humour,
that, when pressed between the fingers, it resembles
glue of the most tenacious consistence, but at the
same time of astonishing transparency.

§ 264.

The remaining portion of the internal cavity of
the eye, is filled up by an exceedingly limpid
aqueous humour, and, by the expanded orbicular
curtain of the iris, is divided into two chambers:
these are, the anterior, or more capacious cham-
ber, which separates the cornea from the iris, and
the posterior one, of smaller dimensions, extending
from the uvea to the corpus ciliare.