The circulatory phenomena are of two kinds in the capillary system:
1st, there is the motion of the fluids; 2d, the alterations which they
undergo.
_Motion of the Fluids in the Capillary System._
These fluids are, 1st, the blood; 2d, others differing from it in their
composition, though we only know their differences of appearance. Let
us examine the laws of the motion of each kind.
The blood, after it has entered the capillary system, is evidently
beyond the influence of the heart, and only circulates by that of
the tonic forces, or the insensible contractility of the part. If we
examine the phenomena of this capillary system but little, we shall
be easily convinced of this truth, which Bordeu first taught. The
capillary system is really the boundary, beyond which the influence of
the heart does not extend. Hence why all the vessels that go out of
this system, exhibit in the fluid they contain a motion that does not
correspond with that of the arteries that go to it. 1st. After what we
have said, there is no doubt of this, as it regards the veins. 2d. It
is also true as it respects the excretories. The increase of secretions
does not correspond with the increase of the action of the heart, nor
does their diminution with the diminution of the pulsations. Who does
not know, on the contrary, that often in a violent paroxysm of fever,
in which the agitation of the arterial blood is very great, all the
glands seem to shut up their ducts and not to pour out any fluid? 3d.
It is the same with all the exhalations; it is not when a fever is the
greatest, that we sweat the most, but when it is somewhat diminished.
Hemorrhages are evidently but an exhalation; now who does not know,
that the pulse is often very weak, when the blood flows abundantly from
the mucous surfaces of the womb, the nostrils, the bronchia, &c.? Who
does not know on the contrary that in extreme agitations of the heart,
most often the blood does not flow by the exhalants? Is the quickness
of the pulse increased during menstruation? It is the redness of the
capillary system, the abundance of the blood of this system, which is
often, as I have said, the forerunner of active hemorrhages; but it
is never the increase of the action of the heart. Oftentimes fungous
tumours, soft flesh that shoots up in wounds of a bad nature, polypi,
&c. pour out blood; the heart has nothing to do with these hemorrhages,
they come evidently from the capillary system. Who does not know, that
frequently when the exhalants pour out copiously serous fluids upon the
membrane of that name, in the production of dropsies, the heart is,
like all the other parts, in a state of real inertia?
Since then all the vessels going from the capillary system exhibit in
their motions no sort of harmony with those of the heart, it is evident
that the influence of this organ is interrupted, is terminated at the
capillary system.
Observe nutrition; it is clearly the capillary system that distributes
everywhere the materials that it has received by the impulse of the
heart; now the influence of this does not extend to the place where the
nutritive matter is deposited. In fact, its impulse everywhere equal
and uniform, pushes the blood with nearly an equal force to all parts,
with some exceptions in the fœtus. Now nutrition is on the contrary
extremely unequal; at one age, it is one part that takes more increase,
consequently receives more nutritive matter; at another age, it is
another organ. This inequality, is the first and principal phenomenon
of growth.
How can we reconcile with the sole and uniform impulse of the heart
in all parts, inflammation, the production of herpes, of different
eruptions, &c. which appear in some places? Would inflammation exhibit
so many aspects, according to the system it seizes, if the heart alone
presided over its development? All the difference between catarrh,
erysipelas, phlegmon, &c. would disappear; and there would be only what
arose from being nearer, or further from the heart.
Let us cease then to consider this organ as the sole agent which
presides over the motion of the great vessels and the small, which,
in these last, driving the blood abundantly to a part, produces there
inflammation, which by its impulse causes the different cutaneous
eruptions, secretions, exhalations, &c. The whole doctrine of the
mechanicians rested, as we know, upon the great extent which they gave
to the movements of the heart.
There are evidently two kinds of diseases in relation to the
circulation; 1st, those that affect the general; 2d, those that affect
the capillary circulation. Different fevers form especially the first
kind. Different eruptions, tumours, inflammations, &c. produce the
second; now, though many relations connect the second with the first,
it is not essentially dependant upon it; the following is the proof of
this; fevers can evidently only exist in animals with great vessels,
in those in which the fluids move in a mass; they cannot take place
in zoophytes and plants, which have only a capillary circulation;
yet these last classes of animals and all vegetables are subject to
all the affections that disturb the capillary circulation. Thus we
see upon plants many tumours; their wounds unite; two portions even
contract adhesions, as a graft proves. The diseases of their capillary
system are no doubt different from those of animals in their progress
and their nature; but they exhibit always the same general character,
because they are derived from the same properties, organic sensibility
and insensible contractility.
Since the diseases of the capillary system are not essentially
connected with those of the general vascular system, they are not
then dependant on it; the circulation of the first is but indirectly
subordinate to that of the second. Hence why the two circulations can
be separate; why more than half of the organized beings have only the
capillary. This is the most important, since it immediately pours out
the materials of nutrition, of exhalations, of absorption: thus it
exists in all organized beings. We cannot conceive of any one without
it, because we cannot conceive of any one that is not continually
composed and decomposed by nutrition.
From what we have thus far said, it is evident, that the blood after
it has arrived in the capillary system, is moved there only by the
tonic influence of the solids; now, as the least cause alters and
changes their properties, it is subject there to an infinity of
irregular motions. The least irritation makes it recede, advance,
deviate to the right, or the left, &c. In the ordinary state, it moves
generally in an uniform manner from the arteries towards the veins;
but at every instant it may find causes of irregular oscillations in
its innumerable anastomoses; hence, as we have seen, the necessity of
these anastomoses. These irregular oscillations in the motion of the
blood in the capillary system, can be seen with a microscope. Haller,
Spallanzani and others, whose experiments are too well known for me
to relate them here, saw them a hundred times. They saw the globules
advance, recede, move in many different directions in animals with
red and cold blood, when they irritated the mesentery or any other
transparent part. In animals with red and warm blood, in those even
whose mesentery is almost as transparent as that of the frog, as in the
guinea-pig, it has appeared to me infinitely more difficult to trace
the motion of the blood in the capillaries.
It is easy to see that all the phenomena of inflammation, of different
eruptions, of tumours, &c. are especially founded upon this
susceptibility of the blood, in the capillary system, to move in an
infinite variety of directions, wherever irritation calls it.
From what has been said, it is evident that there are times when the
blood passes with less rapidity through the capillary system, and
there are others, when it moves more quickly. How then is the relation
always preserved the same, between the arterial and the venous blood?
It is in this way; the irregular oscillations hardly ever take place
except in one part of the capillary system; in no case is the whole
of it affected; thus if the blood moves more slowly in the cutaneous
capillary system, its velocity is increased in the cellular, the
muscular, &c.
This is in fact an invariable law in the vital forces, that if on the
one hand they increase in energy, on the other, they diminish; we might
say, that there was only a certain quantity in the animal economy,
that this might be divided in different proportions, but it cannot be
increased or diminished. This principle results so evidently from all
the phenomena of the economy, that I think it unnecessary to support
it by numerous proofs; now, taking this as incontrovertible, it is
evident that one portion of the capillary system increasing its action,
only at the expense of the others, the sum total of blood transmitted
from the arteries to the veins remains always nearly the same. All the
systems are then, in this respect, supporters of each other; if nothing
passes by the capillaries of one, it is the same thing, provided the
capillaries of another transmit double the amount of fluid that they do
in an ordinary state.
Observe the blood in the cutaneous capillaries before the paroxysm
of intermittent fevers; it recedes from these capillaries; all the
surfaces that it reddened, become pale; the capillaries of the other
systems supply the momentary defect of the action of these. Who knows
if, in many cases where the skin becomes very red, when much blood
enters it, there is not in the other systems a paleness analogous to
that of the skin during the cold fit of fever? I not only think this
very probable, but I have no doubt of it. The external capillaries
certainly contain more blood in summer, whilst those of the internal
systems receive more in winter. There is then continual varieties in
the mode of the passage of this fluid through the general capillary
system; each system transmits by turns, more or less, according as it
is affected.
When we see the glands, frequently in a short time pour out an
enormous quantity of fluid, the serous, cutaneous, mucous exhalants,
&c. furnish also much greater proportions than in a natural state,
we are astonished that the circulation can at the same time continue
with the same regularity; we are not less so undoubtedly, when we see
on the contrary all the evacuations suppressed, and nothing goes out
from the animal solids; now in all these cases, it is the capillary
system, whose forces differently modified in the different parts,
re-establishes the general equilibrium which would inevitably be lost,
if the heart was the agent of impulse which pushed to the extremities
the secreted and exhaled fluids, and transmitted the black blood to the
veins.
Sometimes however a derangement almost universal takes place in the
capillary system, especially on the exterior; this takes place in
sudden changes of the air. Though the vital laws preside essentially
over the capillary circulation, yet the degree of pressure of the
surrounding air can modify it to a certain point; we have a proof of
this in cupping glasses, or in any other means that produce suddenly
a vacuum upon a part of the body; then the fluids pressed in the
neighbourhood by the external air, and not compressed on the contrary
at the place of the cupping glass, raise up and distend considerably
the skin. The sudden changes of the atmosphere produce upon the whole
body, though in a less degree, the effect of a cupping glass. If the
air is rarefied, the whole external capillary system is more full; even
the sub-cutaneous veins swell; a very considerable part of the blood
experiences then a derangement in its motion, between the two systems
with red and black blood. The harmony, the correspondence of these two
systems is disturbed; hence the uneasiness, the sense of weight, &c. of
which we are instantly relieved by a sudden change of the atmosphere.
The evacuation of the blood also establishes differences, though less,
in the capillary system. Bleeding is of two kinds; one lessens the
blood of the circulation of the great trunks; and then it is sometimes
red, as in arteriotomy; but most often it is the black, that is drawn
off; the other takes blood from the capillary circulation; this is
done by leeches, cupping, &c. Each produces a different change in the
course of the blood. Physicians formerly were desirous of knowing from
which vein they ought to bleed. I think it is much more important to
know when we should by bleeding, act upon the general circulation, and
when upon the capillary. In many local congestions, I do not think
that you can diminish the quantity of blood in a part of the capillary
system, by diminishing the mass of this fluid in the great trunks; you
might take a quarter at least of the blood that there then was in the
economy, if the part is irritated, the blood will still flow as much to
this part. On the contrary, you may double by transfusion, the mass of
this fluid in an animal, local inflammations will not arise, because
there must be a preliminary irritation before the blood flows towards,
and enters a particular part of the capillary system.
The fluids differing from the blood which circulate in the capillary
system, 1st. are evidently like it beyond the influence of the heart.
2d. The influence of the tonic powers presides over their motions. 3d.
They are consequently subject to irregular oscillations, according as
the capillaries are differently affected.
We know not the nature of most of these fluids, because they cannot
be subjected to our experiments. They are those that enter the
ligaments, the tendons, the aponeuroses, the hair, the cartilages, the
fibro-cartilages, a part of the cutaneous, mucous, serous surfaces,
&c. They communicate with the blood from which they arise, by the
capillary systems, they afterwards move in their own systems. In most
of the organs in which they exist alone, as in those called white,
they are very slow in their motion, because the sensibility of these
organs is obscure and dull. Thus different tumours, to the formation of
which they contribute, have, as we shall see, almost always a chronic
progress.
There are often in the animal economy those tumours, that are commonly
called lymphatic, though we are wholly ignorant of the fluids that
form them. They are found especially in the neighbourhood of the
articulations; but sometimes only the cartilages, the cellular texture,
the bones, &c. are the seat of these white tumours; it is important
to ascertain the characters that distinguish them from the tumours in
which the blood especially enters.
_Phenomena of the Alteration of the Fluids in the Capillary System._
We have just treated of the phenomena of the motion of the fluids in
the general capillary system; let us now speak of the changes which
they undergo there in their nature.
The blood exhibits a remarkable phenomenon in the general capillary
system; from red, which it was in the arteries, it becomes black. How
does this take place? It evidently can happen only in two ways, viz.
either by the addition or subtraction of some principles. Is it charged
with carbon and hydrogen? Does it deposit only oxygen in the organs?
Are these two causes united to give it its blackness? I think that it
will always be difficult to decide upon these questions, which do not
appear to me to be capable of any positive experiment. However, when
we see the arterial blood furnish all the organs with the materials of
their secretion, nutrition and exhalation, it is to be presumed that it
leaves in these organs, rather than takes from them, the principle of
its colour.
Sometimes the red blood passes through the capillary system, without
losing its colour; for example, when the blood has flowed for a long
time black from a vein, we sometimes see it come out red, or nearly so,
just before it ceases to flow. In opening the renal vein, I have two or
three times made this observation, which has, I think, been noticed by
some authors.
The blood becomes more or less black in the general capillary system.
If you have observed bleedings, you have undoubtedly seen in diseases
innumerable varieties in the colour of the blood that comes from
the vein. Has this fluid a different blackness in each part of the
capillary system? It has appeared to me that the difference is not
very great in this respect. I have frequently had occasion to open the
renal, saphena, jugular veins, &c. the blood has appeared to me to be
everywhere of nearly the same colour. I wished to see if the blood
returning from an inflamed part was more or less black; I made then
in the hind leg of a dog a number of wounds near each other, and left
them open to the air. At the end of three days, when the inflammation
appeared to be greatest, I opened high up on the diseased and the sound
limb, the saphena and the crural veins, in order to examine their blood
comparatively; I could discover no sensible difference. I bled a man
who had a whitlow with an inflammatory swelling of the whole hand,
and the inferior part of the fore arm; the blood appeared of the same
colour as usual. Yet, as the veins bring also the blood of parts not
inflamed, more minute researches must be made.
An object which deserves to be determined with precision, is this, viz.
the cases in which, in general diseases, there is an alteration in the
deep colour of the blood, and the symptoms which correspond with these
alterations. At present we only know that it is more deep coloured in
some cases and less so in others.
IX. _Of the Capillaries considered as the seat of the production of
Heat._
Every one knows the innumerable hypotheses that were made upon the
production of animal heat by the mechanical physicians. Modern
chemists, in showing the insufficiency of these theories, have
substituted one that has not less difficulties. The lungs are
considered by them as the place in which the caloric is extricated,
and the arteries, a kind of tubes, that carry the heat to all parts of
the body. The production of this great phenomenon belongs then wholly,
according to them, to the pulmonary capillary system. I believe, on the
contrary, and I have taught in my courses on physiology, that it is in
the general capillary system that it has its seat.
I shall not stop to refute the hypothesis of the chemists. When we
place on one side, all the phenomena of animal heat, and on the other,
this hypothesis, it appears so inadequate to their explanation, that
I think every methodical mind can do it without my assistance. These
phenomena are the following:
1st. Every living and organized being, both animal and vegetable, has
a temperature of its own. 2d. This temperature is nearly the same
in all ages in animals. 3d. It is entirely independent of that of
the atmosphere; it remains the same in a warm as in a colder medium.
4th. Caloric is often disengaged in health more abundantly in some
parts than in others. 5th. In inflammation there is evidently a more
considerable extrication of it. 6th. The vital forces, especially the
tonic power, have a very decided influence upon the extrication of
caloric. 7th. Each organ has its own temperature, and it is from all
these partial temperatures, that the general one arises. 8th. There
is oftentimes an immediate connexion between the respiratory and
circulatory phenomena, and those of the production of heat; the first
increasing, the second increase also in proportion. At other times this
relation does not exist.
If, below these phenomena, you place the theory of Lavoisier, Crawford,
&c. I do not believe you can make it accord with them, and conceive how
caloric, disengaged in the pulmonary capillary system can be spread,
as they say, through the whole animal economy. By admitting on the
contrary that this fluid is disengaged in the general capillary system,
it is easily understood. But let us explain this way of understanding
the production of animal heat.
The blood draws from two principal sources the substances that repair
the losses it has sustained. These sources are, 1st, digestion; 2d,
respiration; the first pours chyle into the blood, the other mixes
it with different aerial principles. Sometimes cutaneous absorption
introduces into it different substances. The mixture of the blood with
the new substances it receives, constitutes sanguification. Now these
new substances carry continually into this fluid, new caloric; for as
all bodies are penetrated by it, there can hardly be an addition of
a substance to the blood, without the addition of this principle. In
sanguification, caloric combines then with the blood, but it is not in
a free state; it becomes part of the fluid; it is one of its elements.
Thus charged with combined caloric, the blood arrives in the capillary
system; there it gives it out, wherever it undergoes changes. It is
in fact in this system that it is changed into nutritive substance,
into that of the secretions, exhalations, &c. All the functions in
which this fluid changes its nature, in which certain principles are
separated from it, to form certain substances destined especially
to particular uses, necessarily disengage its caloric. I cannot
say precisely how this happens, whether it is more in the internal
alterations that the blood undergoes in furnishing nutrition, or in
those destined to furnish secretion or exhalation. This only is the
general principle, and exhibits three things; 1st, the entrance of
caloric into the blood, with all the substances that repair its losses;
2d, the circulation in a combined state of the caloric newly entered;
3d, extrication of this combined fluid, to form free caloric by the
changes and different alterations that the blood undergoes in the
general capillary system, in forming the materials of the different
functions.
The extrication of caloric is, then, a phenomenon exactly analogous to
those of which the general capillary system is the seat. In nutrition,
in fact, there is, 1st, a combination of new foreign substances with
the blood; 2d, circulation in the great vessels of these substances
combined; 3d, separation of the nutritive substance to enter the
organs. So also the elements of the secreted fluids combine, then
circulate combined, then leave the blood to be thrown out. So, in fine,
every exhaled fluid combines, circulates, and is then separated from
the blood.
From this it is evident that, 1st, the entrance of foreign substances
into the blood by respiration, by digestion or even cutaneous
absorption; 2d, the combination of these substances with the blood
in sanguification; 3d, their circulation in the arterial system, are
three general phenomena common to secretions, exhalations, nutrition,
and calorification, if I may be allowed the term; for the production
of heat is a function and not a property; hence why I think the word
caloricity does not express it.
The caloric arrives, then, in the capillary system combined with the
matter of secretions, exhalations, and nutrition. The blood is the
common fluid that results from all these combinations. In the general
capillary system each part is separated; the caloric to be distributed
over the whole body and afterwards pass out; the fluids of the
secretions go out by the glands; those of exhalations escape from their
respective surfaces; those of nutrition remain in the organs.
It seems to me, that the explanation which exhibits nature always
pursuing an uniform course in her operations, drawing the same results
from the same principles, has a greater degree of probability than that
which shows her separating, as it were, this phenomenon from all the
others, in the way which she produces it.
The manner in which caloric enters the body, is of no consequence.
Vegetables that have no lungs, but only air tubes and absorbents,
and fishes that have branchiæ, have an independent temperature. That
heat may be produced, it is sufficient that foreign substances are
continually assimilated to the fluids of organized bodies, and that
after this assimilation, these fluids, whether they are blood, as in
animals with red blood, either warm or cold, or whether they are of a
different nature, as in those with white fluids and in plants, it is
sufficient, I say, that the fluids undergo different transformations in
the capillary system.
Respiration combines more caloric with the blood; there is consequently
a greater disengagement of this principle in animals who breathe by
lungs, than in others; and even in the first, the greater the lungs,
the greater is the quantity of caloric disengaged; as is proved by
comparing birds, quadrupeds, the cetaceous tribe among fishes, &c.
But these varieties are certainly only in relation to the degree of
temperature; hence there are animals with cold blood, and those with
warm. The general phenomena of the disengagement of heat remain always
the same in animals with lungs, in those without them, and in plants.
From these principles, it is easy to understand most of the phenomena
of animal heat.
The disengagement of caloric is always subordinate to the state of
the vital forces. As the tone of a part is greater or less, it is
more or less warm. This dependance of the heat upon the state of the
forces of the part, is a fact, that is proved by all diseases and
all the phenomena of health; it is as true with regard to heat, as
it is with regard to the exhalations and the secretions. The greater
afflux of blood to an inflamed part and the greater disengagement of
caloric, the increase of this disengagement in the womb and the nose,
and menstruation and the active nasal hemorrhages, &c. the heat of
the chest and active pulmonary hemorrhages, &c. are the effects of
the same cause, viz. the increase of the vital forces of the part. In
general, whenever the tone is much increased, the heat increases also;
hence why there is a greater disengagement of it in almost all active
sweats, hemorrhages, and even secretions; whilst this fluid is not
superabundant in sweats, hemorrhages, or secretions that are called
passive, whatever may be the quantity of fluid separated from the blood
by them.
Each system has its own degree of heat. There is certainly less caloric
given off in the hair, the nails, and the epidermis, than in the
other systems. The white organs, as the tendons, the aponeuroses, the
ligaments, the cartilages, &c. have probably less than the muscles.
Examine the claws of birds, in which there are only these white parts;
they are not so warm as the rest of the body.
The difference of the heat of each system situated in the interior
has not yet been analyzed; I am persuaded that if it was done with
precision, by insulating those which can be, so that they might
communicate by the vessels, we should observe that each separates a
different quantity of caloric, and that consequently there are as
many distinct temperatures in the general temperature, as there are
organized systems.
I am convinced that the ligaments, the cartilages, &c. approximate in
this respect the organs of animals with cold blood, and that if man
was composed of organs analogous to those, his temperature would be
much inferior to what it naturally is. The systems which disengage more
caloric communicate it to those that disengage less. If the hair was in
the middle of the body, it would be as warm as the neighbouring parts,
though its temperature would be independent; it is now always inferior
to that of the body, because it is insulated. Each system has then its
peculiar mode of heat, as each has its peculiar mode of secretion, each
exhalant surface its peculiar mode of exhalation, each texture its
peculiar mode of nutrition; and all this depends immediately on the
modifications that the vital properties have in each part.
It is in consequence of this peculiarity of heat in each system, that
each gives a different sensation in inflammation. Compare the sharp and
biting heat of erysipelas with that of phlegmon; certain dull, obscure
heats, the forerunners of organic affections, with the acute heats
of different inflammations; apply the hand to the skin in different
fevers, you will see that each is almost marked by a particular kind of
heat. Animal bodies alone exhibit these varieties of nature in heat;
minerals have only varieties in degree.
We understand from the principles explained above, not only the
local alterations of heat, but also the general derangement that
takes place in its disengagement, from the effect of diseases,
whether this disengagement is increased, diminished, or affected with
irregularities, as in certain ataxic fevers, in phthisis, when the
palms of the hands and the face are warmer in some cases, &c. Who does
not know that oftentimes when the extremities are frozen, the patient
feels an extraordinary internal heat? It is sufficient that the forces
of the capillary system be differently modified, that the heat may be
so also.
Observe, in fact, that the alterations of heat in diseases are as
frequent as those of the exhalations and secretions, and that they
always present, like the first, a previous derangement in the vital
forces. If chemists apply their theories to these morbid changes of
heat, instead of considering them as a necessary consequence of the
state in which the vital forces are then found, they will necessarily
find in them an insurmountable obstacle.
When we run swiftly, when the blood is violently agitated in the
paroxysm of fever, more caloric is disengaged than at any other time.
Does this prove that it is the general circulation which contributes
to the disengagement of caloric, and that it takes place in the great
vessels? No more than a copious sweat proves that the heart drives it
out. Strongly excited by the shock of the red blood which is suddenly
increased, the capillary and exhalant systems are compelled to
increase their action; now a double effect is the result; 1st, greater
disengagement of caloric; 2d, increased exhalation.
If the heat is increased when respiration is hurried, it appears to
depend only on this, that the latter is hardly ever accelerated,
without the circulation being so too. This is so true, that if you make
for a long time rapidly successive inspirations and expirations, the
heat will not increase. Besides, why should the heat actually increase
by the hurry of respiration? Undoubtedly because more air entering in
a given time, the lungs would absorb more oxygen, and consequently,
according to the opinions of the chemists, more caloric would be
disengaged. But let them present more or less of this principle to the
blood, it absorbs the same quantity. In ordinary inspiration the air
contains much more than can pass into this fluid. When an animal is
made to breathe it pure, the blood does not become more red, because
the same quantity always enters it. So you may in vain put into the
alimentary passages four times more nutritive substance than common, no
more chyle will be formed, the lacteals will absorb no more; there will
only be more excrements, or vomiting will take place.
The state of respiration has no influence then upon the actual heat of
the body; it only contributes to it by constantly introducing a greater
or less quantity of combined caloric. It is thus that animals which
respire the most, have habitually the most caloric.
How can an animal, breathing a very cold air, eating aliments almost
deprived of caloric, &c. in northern latitudes, have as much heat as in
hot climates? It is not the free caloric contained in the parts, but
the combined, which, being introduced into the blood with the foreign
substances, furnishes the materials of that which is disengaged in
the general capillary system. Now the combined caloric is absolutely
independent of temperature. As much fire is elicited from the same
stone by the steel, in the coldest as in the warmest countries.
All the caloric that is combined with the red blood is not disengaged
whilst this fluid is passing through the general capillary system;
there remains some of it still combined with the black blood. Hence
why in the first moments of asphyxia, before death has taken place,
though in consequence of the interruption of respiration, all the
blood that comes through the arteries to the capillaries is black, the
heat continues to be generated for some time. When the contact of the
black blood has even interrupted all the great functions, those of the
brain, of the muscles, the heart, the lungs, &c. it appears that the
black blood then undergoes for some time, a kind of oscillation in the
capillary system, by which it disengages a little caloric. Hence,
why those who have died of asphyxia produced by charcoal, or hanging,
animals killed in vacuo, apoplectics, &c. preserve their heat a long
time after death, as all physicians have observed.
This phenomenon is not however peculiar to the case of which we are
treating. In opening dead bodies at the Hotel Dieu, I have observed
that the time in which they lost their animal heat was very variable;
that a body continues warm a greater or less time, especially among
those who have died suddenly of an acute affection, in the paroxysm
of an ataxic fever, for example, or by a fall, for those who die of a
chronic disease, lose almost immediately their caloric. The difference
in the first is often three, four, or even six hours. This phenomenon
arises from the fact, that whenever death is sudden it interrupts only
the great functions; the tonic action of the parts continues for a
greater or less time after. Now this action disengages a little caloric
from the blood that is in the general system. Thus in violent deaths,
absorption continues some time after death; thus the muscles still
contract; thus perhaps the glands, take up for some hours, from the
blood that remains in the capillary system, the materials proper for
their secretion.
This inequality in the heat of dead bodies can only arise from the
cause I have named; for when the disengagement of caloric has ceased in
the body, that which remains in it becomes in equilibrium with that of
the external air, according to the general laws of this equilibrium.
Now these laws being uniform, their effect would be the same in
every case. Hence then the phenomena related above, are evidently
incompatible with any other theory than that which supposes the caloric
to be disengaged in the general capillary system.
Sympathy has, as we know, the greatest influence upon heat. According
as this or that part is affected, there is disengaged in others more
or less of their fluid. An icy coldness often takes place in syncope.
Ulcerations of the lungs produce a burning in the palms of the hands.
In other affections, the head seems to be the seat of the greatest
heat. In a fever frequently the patient is hot in one place and cold in
another. How does all this happen? in this way; the affected organ acts
sympathetically on the tonic forces of the part; these being raised,
more caloric than usual is disengaged; it is precisely the same as in
sympathetic secretions or exhalations. Whether the vital forces are
raised by a stimulus directly applied, or by the sympathetic influence
they receive, the effect that results from it is exactly the same.
It is necessary to distinguish this sympathetic increase of heat, from
those that are produced by an aberration of perception, as when we
think we are very hot or cold in a part, or experience even a sensation
exactly analogous to those that are natural, though the part to which
we refer this sensation may be in its natural state, there being
neither more or less caloric disengaged in it. It is as when we think
we feel pain in the amputated extremity of a limb. It is an aberration
of perception; it is truly a sympathy of animal sensibility, whereas
the preceding is a sympathy of insensible organic contractility or
tone. It is this last property that is affected; the disengagement of
caloric is a consequence; it takes place as usual, like the perception
that indicates its presence. Another person's hand applied on the
part, feels nothing new in the first case, of which I shall say more
in the following systems; it experiences a warmer sensation in this.
So if the effect of the sympathetic influence is to diminish the tonic
forces, there will be a less local disengagement of this fluid, which
will be equally perceptible to the individual and to any other person
who applies his hand to the part. Diseases continually furnish us with
examples of these phenomena in relation to heat, and no other theory
than the one now given would be able to explain them.
There is a phenomenon that is as difficult to be well understood by
this theory as any other; it is the faculty animals have of resisting
external heat. Every inert body is of the same temperature as the
medium which surrounds it. Every organized body on the contrary repels
the caloric that tends to raise it to a higher temperature than its
own. Perhaps this belongs to the laws of the propagation of caloric, of
which we are ignorant.
It will be asked undoubtedly why in the ordinary state there is only
disengaged a certain quantity of caloric, so as to produce an uniform
temperature of a certain number of degrees of the thermometer. I answer
that it is by the same cause that in the ordinary state the pulse
beats nearly the same number of times in a minute, which makes common
respiration consist of so many elevations and depressions of the ribs,
&c. &c. It is one of those phenomena that belongs to the immutable
order first established, and which it is impossible to explain. Only
it appears that this immutable order depends upon the primitive type
that has been impressed upon the vital forces, a type, which when
nothing excites or diminishes them, produces always phenomena nearly
uniform; but as a thousand causes make them vary, a thousand times
the pulse, respiration, heat, &c. are capable of differing. I would
observe however in regard to the last, that its variations are not so
great as those of many of the other functions. Compare, for example,
the ordinary quantity of secreted and exhaled fluids, with the increase
that takes place under certain circumstances, the common state of the
pulse with its exacerbations in many fevers, &c. you will see that
between the natural and the morbid state there is often an enormous
difference. The heat on the contrary, is never raised but a few degrees
above the temperature of the body. When there appears by touching the
parts, to be a great difference, the thermometer proves that it is in
reality trifling.
I would remark, in concluding this article, that I have not sought
to ascertain how the caloric is disengaged in the capillary system,
what portion escapes, in what relation it is with the red and the
black blood, &c.; none of these can be determined by experiment. Let
us be content in our theories with establishing general principles,
especially analogies between functions that are known, and those
which we attempt to explain, let us attempt merely to offer some
general views; but let us never hazard precise explanations. Some have
endeavoured lately to determine accurately what quantity of oxygen
is absorbed, what quantity goes to produce the water of respiration,
what quantity of carbonic acid gas is formed, how much caloric is
disengaged, &c. This precision would be advantageous if it could be
attained; but no phenomenon in the living economy will admit of it, in
the explanations which it occasions. Chemists and natural philosophers
accustomed to study the phenomena over which the physical forces
preside, have carried their spirit of calculation into the theories
they have formed for those which the vital laws govern. But this should
not be so. In organized bodies, the spirit of the theories should
be wholly different from the spirit of the theories applied to the
physical sciences. It is necessary in these last that every phenomenon
should be accurately explained; that, for example, in hydraulics, all
the portions of the fluids should be calculated in their motions; that,
in chemistry, we should know the precise proportion and amount of each
of the elements that are combined in the changes that bodies undergo.
On the contrary, every physiological explanation should give only
general views, approximations; it ought to be vague, if I may use the
term. Every calculation, every examination of the proportions of the
fluids with each other, all precise language should be banished from
it, because we yet know so little of the vital laws, they are subject
to so many variations, that what is true at the moment we study a fact,
ceases to be so the next, and the essence of the phenomena always
escapes us; their general results only, and the comparison of these
results with each other, should occupy us.