the inspection of an animal that breathes proves it even, as I have
just said. I am persuaded also, that like the urine, the respiratory
fluid is then charged with principles which, during summer, pass off
by the skin, though I have not however any experimental data upon
this essential point, which I propose to clear up the approaching
winter. I think even that many colds depend upon this. In fact, many
of these principles thrown out by the mucous surface of the bronchia,
not soluble in the air, like their aqueous vehicle, stagnate upon this
surface, irritate and excite a cough which throws them off. On this
account, we cough much in winter, as we have often occasion to bathe
in summer, when the saline substances, which are accumulated upon the
skin by the exhalation that takes place there, cannot be evaporated by
the air. Hence why also in many affections of the lungs, in which the
mucous glands and the bronchial exhalants do not increase the quantity
of fluid they usually pour out, but only separate with it, on account
of their change of organic sensibility, substances which the air cannot
dissolve, hence, I say, why in these affections there is a constant
cough; for, as I have said, when a substance remains for any time upon
the mucous system, it irritates, and it makes an effort to get rid of
it. I believe that this elucidates the cause of many coughs, which
have been considered as nervous, on account of the small quantity of
expectoration, and which are only a means that nature employs to supply
the want of the evaporation of the air.
I think that physiologists have not paid sufficient attention, either
as it respects the bronchia or the skin, to the part which can be
evaporated, and to that which cannot. Some animals seem to throw out
more of these principles that cannot be evaporated, than man; hence
why it is necessary to curry horses every day, and even to bathe them
often, in order to cleanse their skins which the air would leave dirty.
Fourcroy and Vauquelin have remarked that there is never phosphate of
lime in the urine of these animals; this substance appears to pass out
with the sweat, and to be chrystalized on the surface of the skin, from
which it is removed by friction and water. I can hardly conceive how
the hairs can be the emunctories of it; it appears to me to be more
natural to think from analogy, that it is by the sweat that it escapes.
I presume that the rain, in the natural state is as necessary to these
animals as to plants. The first do not avoid it; many even expose
themselves to it; it serves as a bath for them, removes the saline
particles the air does not dissolve, and washes the skin.
The cutaneous exhalants do not appear to be everywhere equally
abundant. The face and chest contain many of them; we sweat easily in
these places. On the back and the extremities they are less numerous.
It is rare that we sweat on the palms of the hands and the soles of the
feet. Besides this varies remarkably in different individuals. I know
two sisters, belonging to a family in which phthisis has been frequent,
whose chests are however well formed, and who have never had any sign
of an affection of the lungs, and yet when they are warm they always
sweat from the chest. We know that in some the sweat appears most
usually in the face, and in others on the cranium.
Have the nerves any influence upon the cutaneous exhalation? In many
cases of paralysis, the patients sweat from the sound side. I have
attended, for two months past, a man at the Hôtel Dieu, who after
an apoplexy, had hemiplegia so that the left side of the body was
immoveable, and who only sweats from this side, so that an evident line
of demarcation is visible the whole length of the median line. On one
side the skin is dry, and on the other it is very moist. I know cases
are related in which opposite phenomena have taken place; but they do
not destroy the observation that is uniformly made, that the sweat
takes place equally upon the sound and the diseased side. Besides, who
does not know that when the nervous action is annihilated in a limb,
a blister acts upon it as usual? Do convulsions, in which the nervous
action is so much raised, increase cutaneous exhalation? Have the
states of extreme sensibility, in which all the cutaneous nerves are
so susceptible of receiving all impressions, the least known influence
upon sweating? Let us acknowledge then that in cutaneous exhalation, as
in secretion, we know nothing of the nature of the nervous influence,
if it does exist.
_Sebaceous Glands._
Besides the insensible transpiration and the sweat, which are thrown
out by the skin, this organ is constantly lubricated by an oily fluid,
which occasions, when coming out of a bath, the water with which it
does not unite, to collect in small drops upon the body, which greases
the linen when it remains too long in contact with the skin, catches
the dust that is floating in the air, makes, it remain upon the skin,
and retains many foreign substances coming with the sweat from without
or within.
This fluid is in general much more abundant in negroes, whose skin
is on this account disagreeable, than in European nations in whom
it abounds especially in places provided with hair, particularly
on the cranium. If left without dressing, the hair becomes greasy,
unctuous and shiny; it seems even that this abundance of oily fluid is
destined to support their suppleness. Thus art imitates nature in the
preparation of it, and greasy substances almost always enter into the
dressings of the toilet. It appears that there is less of this fluid in
other parts where there are hairs. It oozes in very small quantity from
the soles of the feet and the palms of the hands, no doubt on account
of the thickness of the epidermis. When we wash these last, the water
collects in small drops on the back of them, and not in the palms,
which are easily and uniformly wet; there is never any of it deposited
on the surface of the nails. This cutaneous oil, retained in certain
places, as in the axilla, the perineum, the folds of the scrotum, &c.
becomes mixed there with certain principles of the transpiration, and
often exhales a fetor that is almost insupportable.
This oily fluid, of the nature of which we know but little, is not
like the transpiration or the fat exposed to evident increase and
diminution; it is always found in nearly the same proportion. It
appears to preserve the suppleness of the skin, by preventing it from
cracking. The ancients sought no doubt to imitate its action over the
whole skin, as we imitate by pomatum its functions in regard to the
hair, by the oily unctions which they made upon the body. This we know
was much practised among the Romans.
Whence comes this cutaneous oil? It can be furnished from three
sources, 1st, from transudation; 2d, secretion; 3d, exhalation.
Some have thought that the sub-cutaneous fat oozed through the pores to
form it; but the scrotum which is destitute of this fat is one of the
most oily parts. The skin of the cranium, which is so to the highest
degree, is hardly at all fatty. That of the cheeks which covers much
fat, is scarcely lubricated with it, &c. In emaciation the skin is
often as unctuous as in corpulency, though it is not always the case.
Finally, in all the other functions, physical transudation is proved to
be nothing; would it exist then here alone?
Those who admit the secretion of the cutaneous oil, (and they are the
greatest number,) place the source of it in the small glands that are
called sebaceous, and which they say are every where spread under the
skin. We see some small tubercles upon the convexity of the ear, upon
the nose, &c.; but in most of the other parts it is impossible to
distinguish any thing; we see only the small eminences of which I have
spoken and which make the skin rough; now they have nothing in common
with these glands, the existence of which I do not deny, but which I
confess I have many times in vain sought for.
This has made me think that there is perhaps an order of exhalants
destined to separate the cutaneous oil, and which is distinct from
that of the exhalants which throw out the transpiratory matter. There
is in the cellular texture exhalants for fat and others for serum.
Certainly no gland presides there over the secretion of the fat. It is
the same with the marrow which the exhalants of the medullary membrane
furnish. There is I think as much probability in the supposition of the
exhalation, as of that of the secretion of the cutaneous oil.
Besides, we must not confound this oil, either with that ceruminous
matter which certain glands pour out on the edges of the eyelids and
behind the ears, and which is forced out by pressure in the form of
little worms, or with that whitish substance that is collected between
the glans and the prepuce, and which is so evidently furnished by small
glands.
ARTICLE THIRD.
PROPERTIES OF THE DERMOID SYSTEM.
I. _Properties of Texture._
These properties are much developed in the skin. The alternations
of emaciation and corpulency through which our organs, the limbs
especially, pass sometimes from a determinate size to one double or
even treble, and afterwards return to their primitive state, prove
these properties; and so do all the different tumours, deposits of
pus, external aneurisms, sudden engorgements which accompany great
contusions, aqueous collections in the abdomen, pregnancy, scirrhi,
numerous affections which increase the size of the testicle, hydrocele,
&c. We see in all these cases the skin at first extended and dilated,
then contracting when the cause of the distension has ceased, and
occupying the place in which it was originally circumscribed.
The remarkable separation which the two edges of a wound experience,
that is made by a cutting instrument, is owing to the contractility
of texture. This separation which takes place upon the dead body,
proves what we have already often remarked, viz. that the properties of
texture, absolutely inherent in the organic texture, are foreign to the
vital forces from which they only borrow an increase of energy; thus
the cutaneous retraction is much stronger during life in a longitudinal
or transverse wound. But it is particularly in amputation that we
observe this increase of contractility from the vital action. No part,
not even the muscles retract so much as the skin; hence the precept so
much recommended in this operation of saving the integuments as much
as possible; hence the essential modifications that have been made in
the ancient methods. The muscular retraction is more sudden; but this,
which is more durable, ultimately prevails; so that in the ancient mode
of amputation, where every part was cut at the same level, they had a
conical stump, the summit of which was formed by the bone, in which was
next seen the muscles, arteries, &c. and in which the skin representing
the base, terminated on the side of the limb.
There are however many cases in which the dermoid extensibility is less
than it at first seems to be. For example, in large sarcoceles, the
skin of the neighbouring parts of the scrotum being drawn, is applied
upon the tumour, and makes up for the extensibility that is wanting in
the skin of this part; that of the penis especially is almost wholly
employed to cover the tumour; so that this organ disappears. It is to
the limits placed to the cutaneous extensibility that must also be
referred the following phenomenon; in a wound with loss of substance,
the fleshy granulations, in contracting by the evacuation of the
white substance that filled them, draw the neighbouring skin in order
to cover the wound; now this drawing produces not only an extension
but a real locomotion. Hence why when the skin, naturally tense and
adherent, cannot yield to this locomotion, the cicatrices are formed
with so much difficulty, as we see upon the cranium, the sternum, &c.;
why on the contrary on the scrotum, the fold of the axilla, &c. they
take place with so little; why in dissecting out tumours, it is so much
recommended to save the sound integuments, &c.
When the skin is stretched, the fibres which compose the spaces that
have been spoken of, separate from each other, and these spaces become
broader. Their breadth becomes especially evident on the internal
surface of the dermis; for as all the pores of the external surface
pierce obliquely its texture, the distension of this texture only
diminishes the length of the small canal they form, but does not
enlarge the orifice of it; thus whilst the internal surface contains
interstices of considerable size, this remains uniform, but allows us
to see these interstices, which render it more transparent where they
exist; hence that appearance like marble on the skin of the abdomen of
women who have had many children.
When the skin is contracted, the internal spaces are drawn together
and even effaced. The external surface which has none of these, cannot
diminish so much in breadth, so that there is a disproportion in the
breadth of the internal and external surface; hence, as I have said,
the convexity of the latter in the horny hardening produced by boiling
water; hence also the inequalities and external roughness which
takes place when cold acts powerfully upon us, and which contracts
the dermoid texture. Besides, this phenomenon only takes place when
the contractility is evident in the ordinary state; for if there has
been previous distention, the cells already enlarged, return only in
contracting to their natural state, and there is no disproportion in
the extent of the internal and external surfaces of the skin.
In most of the extensions, there is a diminution of the thickness of
the dermoid texture. It is only when it is dilated by the infiltration
of water in its spaces, as in leucophlegmasia, that it increases in
thickness by diminishing in density. In chronic inflammation, in
engorgement, and in various alterations of which the dermoid texture is
the seat, it loses in part the faculty of stretching; it breaks with
ease when it is distended. This is what happens in some aneurisms,
in those of the aorta especially that have produced an absorption of
the sternum. A slow inflammation seizes upon the skin that covers the
tumour, and it breaks with a degree of distention infinitely below what
it bears in a sound state, if the death of the patient does not prevent
this fatal rupture, two examples of which I have seen in the ward of
lying in women at the Hôtel Dieu. In this state of inflammation, the
distention is very painful, whilst it is not so in the ordinary state.
The skin loses also its contractile power in most of the chronic
affections of which it is the seat, and which alter its texture.
Are there some days in which the skin is more contracted, and others
in which it is looser and more expanded? I believe so, from observing
the marks left after small-pox, which are much more apparent and deeper
some days than others.
II. _Vital Properties._
These are strongly marked in this system. We might say, that nature
by giving an excess of life to this dermoid covering, has wished to
establish a striking line of demarcation, and to make us perceive the
difference between the inorganic bodies with which its external surface
is in contact, and the organized textures that its internal surface
covers. I shall consider these vital properties as in all the other
systems; some belong to animal life and others to organic.
_Properties of Animal Life._
The animal sensibility exists in the highest degree in the skin. It
presides over the feeling, which is more acute and delicate there than
in most of the other textures. It is also the cause of touch, a double
function which is very different.
The feeling is the faculty of perceiving the impression of the
surrounding bodies. It gives us the sensations of heat and cold,
moisture and dryness, hardness and softness, &c. It has relation then,
1st, to the existence; 2d, to the general modifications of external
bodies. Its exercise precedes that of all the other senses which
cannot be exercised until after its action. It is necessary to the
sight, to hearing, smelling and the taste, as it is to the touch. It
depends only upon a particular modification of the animal sensibility;
it is nothing but this property considered in exercise. Thus when the
particular modifications of this sensibility which preside over the
other senses have been destroyed, when the eye is insensible to light,
the ear to sounds, the tongue to tastes and the pituitary membrane to
odours, these different organs still preserve the faculty of feeling,
both the presence of bodies and their general attributes.
The touch has only relation to the particular modifications of bodies;
it is the source of our notions upon their external forms, their
dimensions, size, direction, &c. It differs essentially from the four
other senses.
1st. In this, that it does not require, like the feeling, any
particular modification of sensibility. The hand is a little more
sensible than the rest of the skin; but there is not a great
difference, and we should touch bodies almost as well, if that of
the abdomen covered the phalanges. On the contrary, each sense has a
peculiar sensibility which places it exclusively in relation with a
determinate body in nature. The pituitary membrane would be struck by
light in vain, if placed at the bottom of the eye like the retina;
the palatine membrane if it lined the nasal fossæ, would not perceive
odours, &c.
2d. The touch is exercised only upon masses, more or less considerable
parcels. The other senses are brought into action by the insensible and
infinitely multiplied particles of bodies, as the luminous, savoury
particles, &c.
3d. Most of the other senses do not require the previous exercise of
the will. Odours, light and sounds strike upon their respective organs,
and often produce, without our attending to them, their respective
sensations. It is the same with feeling; the will most commonly has
no part in it. It is exercised because we live in the midst of many
excitements. We do not most often seek for the causes of general
sensations; they are those that come and act upon us. On the contrary,
the touch requires to be produced by an act of the will. It is exerted
in consequence of the exercise of the other senses; it is because we
have seen, heard or felt an object, that we touch it. We confirm or
correct by this sense the notions, which the others have given us.
Hence why it is, as it were, dependant on them. The more they are
contracted, the less frequently is it exercised. The blind, the deaf,
&c. have less desire to touch than him, who has all his sensitive gates
open to the impression of external bodies.
4th. Most of the other senses require a peculiar structure as well as a
peculiar sensibility in the organs which compose them. On the contrary,
the touch only requires a particular form in its organs. Provided that
these have on the one hand animal sensibility, and on the other can
embrace by many points external objects, they can distinguish their
tangible qualities. The touch will be obscure if we grasp bodies in
one or two directions only; yet it will take place. Thus we touch with
the hollow of the axilla, the bend of the arms, hams, &c. with the
lips and with the tongue. Thus the elephant touches with his trunk,
reptiles by twining themselves around bodies, most animals with their
snouts, &c. But the more the points of contact are multiplied, the more
perfectly is the sense exercised. The hand of man is in this respect
the most advantageously formed; it proves that he is better adapted to
communicate with what surrounds him than all other animals; that the
empire of his animal life is naturally much more extended than that
of theirs; that his sensations are more accurate, because they have a
means of perfection that theirs have not; and that his intellectual
faculties are destined to have an infinitely greater sphere, since they
have an organ infinitely better than theirs to perfect them.
The sensibility of the skin resides essentially, as we have seen, in
the papillary body; it is there that all the great phenomena relative
to sensation take place. It is this portion of the skin that truly
belongs to animal life, as the reticular body is, on account of the
vascular plexus that forms it, the portion essentially dependant on
organic life. The chorion being as it were passive, remains foreign to
every kind of important function, and serves only for a covering.
The extremely acute sensibility of the papillary body requires a
covering to defend it from strong impressions. This covering is the
epidermis. When it is removed, every touch is painful; the impression
of the air even is very much so; it is this removal of the epidermis
that produces the smarting that is felt when a blister is taken off.
Observe in fact that smarting is a very frequent kind of pain, which
the animal sensibility of the skin occasions when more raised than
usual. This term[1] is borrowed from burns, which, when they are only
to a certain extent, acting nearly like blisters, lay the papillæ bare;
now as it is always the skin which is exposed to the action of fire,
we transfer to all burnt organs the ideas which we attach to the word
smarting. But the pain is far from having the same character in the
other systems; this peculiar one belongs only to the dermoid, in which
it takes place from a burn, erysipelas, after a blister, &c. and during
all inflammations that have their seat in the reticular body. No other
system when inflamed gives us this sensation. The pain is throbbing
in the cellular; it exhibits a wholly different modification in the
muscular, when it is the seat of acute rheumatism, &c.
[1] In order to understand this sentence it should be observed that
the word which I have translated smarting is _cuisson_, which means
the action of fire upon animal bodies, and is also used for the
painful sensation which this action produces.—TR.
There is another kind of pain which is also peculiar to the cutaneous
system; it is itching, which is the first degree of smarting. We
remove it by a gentle friction, which exciting in the papillæ a
different sensation, effaces that of which they are then the seat;
but when this new sensation has passed off, the former one, which is
occasioned by a permanent cause, is reproduced and requires a new
friction; there happens then in a small way, what we observe in a
large one, when a stronger pain makes us forget one that is weaker. No
other system in the economy exhibits this kind of pain, so frequent in
itch, herpes and many other cutaneous eruptions. In their tubercular
inflammations, the serous membranes become the seat of white eruptions,
analogous to many of those of the skin; the mucous surfaces are also
often affected with many small pimples; now this sensation is never
manifested in either of them.
There is also a sensation which appears to be the minimum of that pain
of which smarting is the maximum; it is tickling, a mixed sensation,
an hermaphrodite, as an author has called it, which is agreeable when
carried to a certain degree and painful beyond it. Carry the fingers
lightly over a mucous or serous surface, a muscle or a nerve laid bare;
an analogous sensation will never arise from the contact.
The animal sensibility of the skin is, like that of the mucous
surfaces, subjected to the essential influence of habit, which can
transform successively into indifference or even into pleasure, what
was at first painful. Every thing that surrounds us furnishes constant
proof of this assertion. The air in the succession of the seasons,
caloric in the numerous varieties of the atmosphere, in the sudden
change from one temperature to another, water in a bath, in the moist
vapours with which the medium is loaded in which we live, our garments
of which some, as those of wool, are at first very painful, every
thing which acts upon the skin by mere contact, produces sensations
in it which habit continually modifies. Observe the mode of dress of
different nations; in some, all the superior extremities are bare;
in others, the fore-arm only appears; the inferior extremities,
either in whole or part, are naked in others; in some, a more or less
considerable portion of the trunk is left exposed to the air, and among
the savages, nothing is covered. The portions which in each people
remain naked, bear the contact of the air, without giving any painful
sensation. Let them expose, on the contrary, parts usually covered,
especially if it is cold, and at first pain will be the consequence of
it; then the parts gradually becoming accustomed to this contact, will
get to be insensible to it. There has been much said latterly of the
danger of the Grecian costumes, of the nudity of females, &c. I do not
speak of the morality of them; but every thing that is reprehensible
physiologically is, that the progress of the fashion has been more
rapid than that of the sensibility. If they had exposed at first the
neck, then a little of the chest, then the bosom, &c. habit would by
degrees have given a new modification to this property, and no accident
would have resulted from it. But in going suddenly from a costume in
which every part is covered, to that in which the superior half of the
chest, either before or behind, remains naked, is it astonishing that
colds, catarrhs, &c. should be the result of it?