obstacle which prevents the internal caloric from suddenly escaping and
thus placing the body in equilibrium with the surrounding medium. This
is evident in countries near the pole. Upon this subject an observation
the reverse of the preceding can be made; it is that the cetaceous
animals inhabit seas the temperature of which is most unlike their
own. Whales are sought for especially in the latitudes of Greenland,
Spitzbergen, &c. Why do fishes with warm blood delight in the frozen
seas, whilst the amphibious animals with cold blood prefer the burning
heat of the sun? I know not.
Let us observe that most of the internal organs when exposed in
solutions of continuity, have not the faculty of preserving as well as
the skin, a degree of independent temperature. They become cold or hot
sooner than it as long as they remain healthy. The intestine brought
out of the abdomen in the operation for hernia, a muscle laid bare, &c.
&c. exhibit this phenomenon; thus in order to give them this faculty of
having an independent temperature, nature inflames them, and they thus
constantly preserve their heat, whatever may be that of the surrounding
medium. The mucous surfaces next to the skin resist the surrounding
temperature the most, as is seen in prolapsus of the rectum, in
inversion of the anus, &c. This difference among the different systems
is probably owing to that of their structure.
6th. When the action of caloric is carried to a very considerable
extent, it begins to act upon the skin, and its effects are the more
evident in proportion as it is the more intense. 1st. The slightest of
these effects is to produce an evident redness, a kind of erysipelas;
the caloric then acts like a simple rubefacient. 2d. The second is to
redden the skin and then to produce vesicles on it. 3d. In the third
there is a real horny hardening, a crisping of the fibres of the
chorion which contract, like those of all the animal textures exposed
to too strong a degree of heat. 4th. In the fourth and last effect,
the dermoid texture is burnt, blackened and reduced to mere carbon.
These different degrees of burning arise only from different degrees of
caloric. I would observe that in the two first effects, this fluid acts
upon the vital forces, and that these two effects cannot consequently
take place except during life. The two last are exerted only upon the
texture of the organ; thus they take place after death precisely as
before. Cooks often employ the horny hardness, to give to the skin a
hardness and brittleness necessary in some kinds of cooking.
7th. Cold carried to a great degree acts also upon the cutaneous organ,
and produces different effects, according to its intensity. The first
of these effects is very analogous to the first effect of a slight
degree of caloric. It consists of a kind of local inflammation. The
tip of the nose, the ears and the fingers, the cheeks, &c. become red
from a slight degree of cold. I have not accurately observed the other
effects between this and the last, which consists in a sudden privation
of life. But there is this difference between the gangrene that then
takes place, and that produced by a high degree of caloric, that the
blackness is sudden in this last, whereas it takes place only as a
consequence in the other. Observe in fact that there is in gangrene
two things which physicians do not sufficiently distinguish, 1st, the
mortification of the part; 2d, its putrefaction. The mortification
is always antecedent; it is produced by a thousand different causes;
sometimes by the ligature of an artery, as in aneurism; sometimes
by that of a nerve; often by violent inflammation; sometimes by a
contusion, attrition, a bruise, &c. Whenever a part is dead in the
midst of those which live, whatever may be the cause of its death, it
becomes putrid precisely like a dead body, every part of which life has
left. Putrefaction takes place then even sooner, because on the one
hand the natural heat of the body, and on the other the moisture of
the surrounding parts, favour it remarkably. This putrefaction varies
according to the state in which the part was at the instant of death.
If much blood infiltrated it, as when inflammation destroys life, it
quickly becomes putrid, blackens immediately and allows a fetid sanies
to escape; this putrefaction is called moist. If there is but little
blood in the part at the instant of death, its putrefaction is less
sudden; it first putrifies, then blackens, and allows but little sanies
to escape; this is the dry gangrene. Thus in a dead body, if one part
is much loaded with blood, as the head of those that have died of
apoplexy, its putrefaction is much more rapid and moist than that of
the parts in which this fluid is less abundant. In the gangrene which
succeeds mortification produced by cold, there is often dryness of the
part, because there was but little blood in it at death. How little
many physicians know of the progress of nature in the employment of
antiseptics, which they apply in the living economy, as upon flesh
without life. Antiseptics are applied for one of two purposes, either
to prevent the death of the part, or its putrefaction. 1st. If it is
with the first intention, antiseptics should be varied. By untying the
artery of a limb of an animal that has been tied, you will perform
an antiseptic operation. Bleeding and emollient applications which
lessen the violence of inflammation in a phlegmon, are antiseptics.
A tonic as wine and all stimulants which excite the vital forces in
a part in which they are languid after a bruise, are antiseptics.
This word is then extremely improper when it is applied to medicines
designed to prevent the mortification of the parts. Antiseptics are
employed to prevent a dead part in the midst of living ones becoming
putrid; some effect is obtained; thus by sprinkling cinchona, muriate
of soda, or any neutral salt, by moistening a limb, a portion of skin,
the extremity of the nose, &c. which is dead from any cause, the
putrefaction will be arrested, as in a dead body upon which the same
means are employed. But what will be the result of it? a little less
fetor in the surrounding parts and less danger of their receiving
the influence of the emanations of the dead part; but it is always
necessary that this should come off; antiseptics will never bring it
to life. Hence it is evident that these means should be considered in
two points of view entirely different. The first prevent mortification,
and vary remarkably though they are designed to effect the same
object; thus our means of curing retention of urine are very variable,
oftentimes opposite, according to the cause which tends to produce this
retention. The others prevent putrefaction, without restoring the parts
to life; now these are uniformly the same, whatever may have been the
cause of the local death.
_Action of the Air._
The air acts incessantly upon the cutaneous organ. In the ordinary
state, it constantly removes from its surface the sweat that is exhaled
from it. Fourcroy, who has paid particular attention to the solution
of the transpired fluid by the surrounding air, appears to me to have
allowed too much influence to this solution upon transpiration. In
fact there are two very distinct things in this function; 1st, the
action of the exhalants which throw out the fluid; 2d, the action of
the air which dissolves and evaporates it. Now the first of these is
wholly independent of the other. Whether the fluid is dissolved or not,
more is still furnished by the exhalants. If the solution does not
take place, the fluid accumulates upon the skin, which remains moist;
but this moisture does not obstruct the exhalant pores and prevent
new moisture from being added to it. A comparison will render this
very evident. In the natural state, the serous fluids are constantly
exhaled and absorbed; the absorbents perform for them the functions
of the air which dissolves the sweat; now, though these vessels cease
to act, as in dropsies, the exhalants continue their action; there
arises only a serous collection, which, though applied to the orifices
of the exhalants, does not prevent them from pouring out more serum.
The bladder in vain contains urine which presses upon the opening of
the ureters, these ducts do not pour less into it. Though the mucous
juices become stagnant on their respective surfaces, new juices are
however poured upon these surfaces. So though the skin remains moist
from the want of solution of the transpiration, more transpiration is
nevertheless exhaled. Solution is a physical phenomenon wholly foreign
to the vital phenomenon of exhalation. We transpire in a bath as well
as in the air; only the fluid which arises from it is mixed with the
water, instead of being reduced to vapour.
The moisture of the skin is owing to two causes wholly foreign to each
other; 1st, to the increase of the fluid furnished by the cutaneous
exhalants; now the action of these exhalants may be increased from
three causes. First, every thing which accelerates the motion of the
heart, as running, the paroxysm of acute fevers, &c. drives to the
skin, as it is commonly expressed. In the second place, every thing
which tends to relax and expand the cutaneous organ by a direct action
exerted upon it by the surrounding bodies, increases also the action of
these exhalants, as in the great heat of summer, as in a bath and after
coming out, as in a heated room, &c. In the third place, the action
of the skin is in many cases, sympathetically increased. Here may be
classed the sweats of phthisis of which the lungs are the source; those
of fear, which depend upon a sudden affection of an epigastric organ;
those of many acute diseases, &c. Now in all these cases, however
active the solution by the air may be, the skin will be constantly
moist, because there is thrown out upon it more fluid than the air can
dissolve. Thus in catarrhs of the lungs, in which more mucous juices
are thrown into the bronchia than the air can remove, it is absolutely
necessary that there should be cough and expectoration to carry off the
remainder.
2d. There are cases in which the moisture of the skin arises from the
solution not being sufficient. This is what takes place in the moisture
of the bed in which the air is not changed, in damp weather, &c.
There is not then more fluid exhaled; but the ordinary fluid becomes
evident, because it is not dissolved. It is under this point of view
that we must consider the action of the air upon the cutaneous organ
which transpires. It carries off nothing in this organ; it has no real
action upon it; it takes only what its vessels throw off. Solution
is merely accessory, it is always subsequent to exhalation, and has
no relation with it. In the same day, in which the temperature has
remained the same, the skin is often dry, moist, humid and even wet
with sweat. If the air acts upon transpiration, it is by contracting
or relaxing the exhalants, and not by dissolving what they throw out.
If the skin formed a sac without an opening, like the serous surfaces,
transpiration would go on though it was removed from the contact of the
air, the same as if in contact with it. Why in fact should not that
take place there, which does upon these surfaces?
If we consider the action of the air upon the skin of the dead body,
we see that it produces two different effects, according to the state
of the body. If the air penetrates the skin on all sides, it dries it,
and it then acquires a sort of transparency, like the fibrous organs,
unless a large quantity of blood had been accumulated in it at the
moment of death, in which case it becomes black or of a deep brown.
Thus dried, 1st, it is firm and resisting, but can be bent in various
directions without breaking, as is the case with many textures thus
dried, as the cartilaginous, the muscular, &c. &c. 2d. It is much less
easily altered than most of the other textures in a dried state. 3d. It
absorbs moisture less easily than them, though however when immersed
for a long time in water, it finally resumes nearly its original colour
and loses its transparency. 4th. It does not exhale a very disagreeable
odour, like many of the other textures. Hence why the skins of animals,
merely dried, are used in many of the arts; why some barbarous people
make use of them for clothing, &c. The aponeuroses, and the mucous,
serous and fibrous membranes could not be thus employed. It is to this
also that must be attributed the little alteration that takes place in
the exterior of mummies, which would never last for ages, if clothed
with a fleshy or serous covering.
When the skin is left upon the dead body, or exposed to a moist air, it
becomes putrid instead of drying. Then it takes at first a dull colour,
then a green and finally a black one. It exhales a very great fetor,
swells and thickens, because the gases which are disengaged there fill
the cellular texture in its little spaces. A mucous covering is spread
upon its external surface, which is deprived of its epidermis. Nothing
similar to this covering is seen on the internal surface. Finally,
when all the fluids it contains are evaporated, there remains a black
residuum, very different from that which is left after combustion.
_Action of Water._
This action during life, is relative either to the substances that
are deposited on the surface of the skin, or to the cutaneous texture
itself.
The sweat deposits incessantly upon the epidermis many substances, the
principal of which are taken away by the air, but many being slightly
soluble in it, as the salts for example, remain on its surface, and
adhere to it when not removed by friction. Mixed with the unctuous
fluid which oozes out upon this surface, and with the different
foreign particles that the air deposits there as everywhere else,
these substances form upon the skin a deposit which cannot, like the
transpiration, be carried off by solution. Now water removes all this
deposit; hence why the use of baths is truly natural. All quadrupeds
bathe themselves. All birds frequently plunge into the water; I do
not speak of those for whom this fluid is as it were the element. It
is a law imposed upon all species of animals whose skin throws out a
considerable quantity of fluid. All the human races hitherto observed
frequently plunge into brooks, rivers, or lakes, along which they
take up their abode. The countries that are well watered are those
which animals prefer. They avoid those where this fluid is wanting, or
in which it is only sufficient for their drink. We oppose nature in
every thing in society. In our own, numerous classes hardly ever use
a bath; thus you must seek especially in these classes for cutaneous
diseases. We have seen that the mucous juices, remaining too long upon
their surfaces, irritate and stimulate them and cause there various
affections. Is it astonishing that the residuum of the cutaneous
exhalation which the air does not remove, should occasion various
alterations upon the skin? In summer, baths are more necessary, because
as many excretions are taking place by the skin, more substances are
deposited there. In winter, in which every thing passes off by the
urine, the cutaneous surface becomes less dirty, and has less need
of being cleansed. After severe diseases, in which there has been
copious cutaneous evacuations, one or two baths terminate the treatment
advantageously. Let us consider water then as acting as accessory to
the air upon the skin, as removing from its surface substances which
the first cannot dissolve, substances, which varying remarkably like
those that compose the urine, have presented the transpiratory fluids
to chemists, sometimes as alkaline, sometimes as acid, oftentimes as
containing salts, sometimes charged with odoriferous substances, &c.
Water is the general vehicle; when it is evaporated, it leaves the
substances that are not volatilized like it. It is on this account that
dry frictions are also advantageous; they clean the exterior of the
body.
As to the action of the bath upon the cutaneous texture, we know but
little of it during life. They say in medicine that it softens, relaxes
and unbends this texture; this is vague language to which no precise
meaning is attached, and which is no doubt borrowed from the relaxation
which the skin of dead bodies undergoes, or even tanned leather, when
exposed to water. A bath acts upon the vital forces of the skin, raises
or diminishes them, as I shall say; but it leaves its texture in the
same state; it is only that of the epidermis which it alters, as we
shall see.
Macerated in water of a moderate degree of temperature, in that of
cellars for example which does not vary, the human skin softens, swells
but little, becomes evidently whiter, and remains for a long time
without experiencing any other alteration than that of a putrefaction
infinitely less than that of the muscular, glandular, mucous textures,
&c. subjected to the same experiment. This putrefaction, which removes
the epidermis, appears to be much greater on the side nearest to this
membrane; at the end of two or three months the skin loses but little
of its consistence. It does not become pulpy as the tendons and muscles
in this length of time when macerated; it does not become a fetid pulp
till the end of three or four months. I have preserved some of it for
eight months, which has still its primitive form, but which feels
liquid under the fingers when pressed a little. In the half putrid
state, the skin still preserves the faculty of crisping from the action
of caloric; it moves about when placed on burning coals, or when
plunged into boiling water. When once reduced to a really putrid state
it loses this property.
Exposed to ebullition, the dermoid texture when well separated from
the cellular, furnishes less scum than the muscular, the glandular and
the mucous; it resembles in this respect the tendons, no doubt because
being almost wholly gelatinous, it contains but little albumen. In the
horny hardening that takes place a little before ebullition commences,
it twists and then always becomes convex on the side of the epidermis,
and concave on the opposite side; and for this reason; the fibres of
the chorion in contracting by the horny hardening, are pressed against
each other; all the spaces which exist between them are effaced; now,
as these spaces are very large in the second direction, the dermoid
texture necessarily becomes more contracted there, whilst in the first,
the spaces hardly existing at all, every thing being almost solid,
the fibres have less space to contract, they remain longer, and the
surface continues larger. In the natural state the cavity of these
spaces, being filled with cellular texture, increases the extent of the
internal surface; this space then disappearing, this surface becomes
contracted.
The moment this kind of twisting takes place upon the skin, it is
covered, as I have said, with an infinite number of vesicles filled
with serum, and which are formed by the epidermis. As this membrane
is very thick on the soles of the feet, and the palms of the hands,
it cannot contribute in those places to their formation, and we see
nothing there similar to them. Yet by removing it from feet that have
been boiled, I have observed that it contained between its layers
many small vesicles, which were scarcely visible. I have not analyzed
the water of these vesicles, but presume it is analogous to that of
blisters. Besides a greater or less quantity of it is poured out, and
the vesicles are consequently larger or smaller, according to the
state of the external capillary system at the instant of death.
By the horny hardening, the skin becomes hard, elastic, very resisting,
thicker, but not so broad. It soon loses its semi-transparency and
yellowish colour, like the boiled fibrous organs. Then the hardness
it had acquired at the instant of the horny hardening is gradually
lost; it softens, gives out much gelatine in the water in which it
is boiled, does not lessen in size, but even increases in thickness.
Every kind of fibre, vacant space and organization is then gone; it
is a membranous mass, homogeneous in appearance, semi-transparent and
gelatinous. In this soft state, it does not lose the elasticity it had
acquired in the horny hardening, like the mucous, serous, cellular
textures, &c. &c. The great quantity of gelatine it contains still
preserves this property in it. The least motion that is communicated to
it produces a general trembling, a sort of vibration of all its parts,
exactly analogous to that of the various kinds of animal jellies, half
coagulated, which vacillate in the vessel from the least jar.
Finally, the ebullition still continuing, the gelatine is almost all
dissolved, and there remains only a residuum like membrane and which
disappears with great difficulty; it requires even a very long time
for common boiling water to reduce the skin to this residuum. Such are
the phenomena of the ebullition of the human skin as I have carefully
observed them. Chemists have paid great attention to the dermoid
texture of many other animals; they have formed different ideas of its
nature; they have admitted that there are two substances in it; one
fibrous and the other gelatinous. I refer to their works upon this
point, particularly to the labours of Seguin, and the work of Fourcroy;
for in general I do not relate what is detailed by others, it would be
only a useless repetition.
_Action of the Acids, the Alkalies and other Substances._
The sulphuric, nitric and muriatic acids act upon the skin, when in
contact with it, as upon all the other animal substances. I have
remarked however that their action is much slower, especially on the
side of the epidermis, though this membrane may have been previously
taken off. The first of these acids reduces it easily to a blackish
pulp; the others bring it to a pulpy state with more difficulty, even
when they are very little weakened; the oxy-muriatic acid produces
hardly any effect upon it.
Some authors have said that the lapis infernalis produces the same
phenomena on the dead as on the living body. I wrapped up in a piece
of skin, as in a rag, many fragments of this substance, so that they
were in contact with the epidermis; at the end of a day they were
reduced to a kind of pap of a yellowish red, by the moisture which they
had absorbed. The dermoid texture, crisped and contracted, had not
been penetrated; it did not appear even to have been injured on the
exterior. In general the action of the alkalies appears to be wholly
different during life, and it varies even according to the different
degrees of vitality. We know that flaccid and fungous flesh burns
much less easily than that which is red and vigorous. It is the same
with the acids. Never during life do they produce any thing analogous
to that pulp of different colours according to the acids that are
employed, which is always after death the result of their action.
We know that an alkaline solution, put in contact with the skin,
produces a kind of unctuous and slippery feel, which is no doubt owing
to the combination of the alkali with the oily deposit of the skin,
from which arises a sort of soap.