Since this system is not destined merely to unite the arteries to the
veins, and change the black blood to red, it is evident that other
fluids besides the blood, must circulate in them; this is in fact what
observation proves. There are many parts in the animal economy, in
which white fluids alone circulate. We know the hypothetical opinions
of Boerhaave upon the white arteries, the decreasing vessels, &c. We
shall find these opinions in all books; I shall only say here what
accurate observation shows us. That there is in the general capillary
system, parts in which the blood especially moves, others pervaded
only by white, or greyish fluids, &c. is a thing of inspection, and
has no need of proofs. But what is the proportion of these fluids in
the different organs? it is this that must be examined; now there are
parts where the blood predominates almost exclusively in the capillary
system, others where it exists in part, and in which there is a portion
of different fluids, others in fine in which these fluids alone are
found.
_Of the Organs in which the Capillaries contain only Blood._
It appears that in the muscular system, in the spleen, in certain
parts of the mucous surfaces, as in the pituitary membrane, &c. the
blood so predominates in the capillary tubes, that almost every other
fluid is unknown in them; thus fine injections demonstrate few other
vessels; the arteries and the veins are seen there in great abundance.
The blood, or its colouring matter, is in them, as I shall say, in two
different states; in one, it stagnates and serves then to colour the
organ; in the other, it circulates and contributes to its nutrition,
its excitement, &c.
_Of the Organs in which the Capillaries contain Blood and Fluids
differing from it._
These organs are the most numerous in the animal economy. The bones,
the cellular texture, the serous membranes, a part of the fibrous
system, the skin, the vascular parietes, the glands, &c. &c. exhibit
this arrangement in a very remarkable manner.
To give an idea of the capillary system in this kind of organs, let us
take one in which it is easy to examine it, the serous membranes, for
example. When we lay them bare in a living animal, their transparency
permits us to see in an evident manner that they contain but very
little blood in their capillary system; there are many branches under
them, but they appear to be only contiguous; raise, for example, in a
small living guinea-pig the peritoneal coat of the stomach; the red
arteries, which at first view appeared to be in this coat, remain
untouched. These membranes, certainly owe their white or greyish colour
to the small quantity of blood they receive from their small vessels,
to which the next trunks give rise. After having thus exposed a serous
membrane, in order to see the quantity of blood that is found in it in
a natural state, irritate it with any stimulant; at the end of some
time, it will be covered by an infinity of reddish streaks, which will
be so numerous, that they will change its whiteness into the red colour
of the mucous surfaces.
Force fine injections into a dead body, they will so fill the capillary
system of the serous surfaces, of those of the peritoneum, for example,
that those surfaces will be wholly black, and appear formed only by
a net-work of vessels, whilst very few are apparent in the living
body, because it is not the blood that fills them. When we cannot open
animals to convince us of this, surgical operations, in which the
intestines are laid bare, the peritoneum being untouched, wounds of the
abdomen, the cesarian operation, &c. will prove incontestably that in
the natural state, the blood fills ten and even twenty times less of
the vessels, upon the serous surfaces, than injections show us in their
texture.
Examine these surfaces in chronic and acute inflammations, of which
they are the seat, in the first especially, they exhibit a vascular
net-work, so full of blood, that their redness is often deeper than
that of the muscles.
All the organs of which I have spoken above, exhibit the same
phenomenon. Observe what takes place in the skin; fine injections show
there infinitely more vessels than are filled with blood in a natural
state; the face of a child well injected, is wholly black. Who does not
know that oftentimes from the effect of passion, the blood fills with
great rapidity, in the skin of the cheeks, numerous vessels, which in a
calm state of mind are not apparent?
Examine the conjunctiva, taken as an example in inflammations;
frequently in a short time it changes its white to a bright red,
because the blood fills vessels, in which it did not before pass; you
can easily distinguish these vessels with the naked eye; you can see
that the blood accumulated in this membrane, is not effused, but that
it is contained in real vessels.
I take for example the organs that have one of their surfaces free from
adhesion, because the state of the capillary system is more easily
distinguished in them; but the others present the same phenomenon; we
shall see that the cellular texture, certain fibrous organs, &c. &c.
examined comparatively, on the one hand in animals that we dissect
alive, on the other in an inflammatory state or after fine injections,
present a much less number of vessels in the first, than the second
case.
It can then be established as an incontestable fact, that in many of
the organs of the animal economy, the general capillary system is,
in the ordinary state, entered in part by blood, in part by other
different fluids, that appear to be white.
The proportions vary singularly; thus the capillary system of the
serous membranes contains hardly any blood as I have said; that of the
skin more; the mucous surfaces still more, &c. But whatever may be the
relation, the difference is not less real in the capillary system.
Perhaps also there are always in this system empty vessels, destined
to receive fluids under certain circumstances; thus the urethra, the
excretory ducts in certain cases, the orifices of the lacteals in the
intervals of digestion, contain nothing. It is difficult to conceive
of the rapidity of the passage of the blood in the capillaries of the
face, and in those of other parts of the skin, if these vessels contain
a fluid, which is to be displaced by the blood. However, nothing but
what is founded upon experiment can serve to decide this question.
_Of the Organs in which the Capillaries do not contain Blood._
These organs are less numerous than the preceding. They are the
tendons, the cartilages, the hair, certain ligaments, &c. Dissected in
a living animal, not a single drop of blood escapes from these organs,
and yet there is no doubt that capillaries exist in them; oftentimes
very fine injections demonstrate them there. Inflammation, also,
frequently fills these capillaries with blood. Into the hair, this
fluid enters in the plica polonica, &c. The non-vascular appearance
of these organs in the living body, is illusory; it is because their
fluids are divided into very small streams, the circulation of them is
more slow, and their colour different from the blood, that we cannot
perceive them.
II. _Difference of Organs in respect to the number of their
Capillaries._
Though the capillaries exist every where, yet they are more or less
numerous in the different organs; in making fine injections, it is easy
to be convinced of this. What anatomist has not been struck by the
prodigious number of vessels in this way developed, upon the skin, the
serous surfaces, the cellular texture, &c. compared with those in the
fibrous organs, in the muscles even, &c.?
I have sought for the cause of this difference, and it has not appeared
difficult to find it, since where injections develop few capillaries,
there is only nutrition going on, as the bones, the muscles, the
cartilages, the fibrous bodies, &c. are a constant proof; on the
contrary, in all those in which many fluids enter, there are, besides
nutrition, other functions, such as exhalation and secretion. Hence why
a serous surface, almost as white as a cartilage in the living body,
becomes ten times darker than it by the same fine injection; why the
skin, compared to the fibrous organs, exhibits the same phenomenon;
why in proportion to the arteries that enter a muscle and a gland, the
latter admits much more injection than the other.
These observations, which are uniform and invariable, prove that the
capillary system is as much more developed in a part, as it has more
functions to sustain. Observe in fine, that it is a kind of depot
in which the fluids remain for a certain time, before serving for
nutrition, exhalation and secretion. Where these three functions are
united, it is necessary that there should be more fluids there, than
where only one of them exists; hence more capillary vessels.
The capillary system is not then in the organs in proportion to their
size; a portion of the pleura contains more vessels than a tendon that
is ten times larger. It is the nutritive substance that fills the place
that these vessels do not occupy.
We might, from what has just been said, divide the systems into two
classes, from the development of their capillaries; place on one side
the serous, the mucous, the glandular, the dermoid, the synovial,
the cellular, &c.; on the other the osseous, the cartilaginous, the
fibrous, the arterial, the venous, the fibro-cartilaginous, &c. The
first class surpasses the second, considerably, in the number of its
small vessels. Observe, also, that inflammation, different eruptions,
all the affections, in which there is, as it is called, an afflux of
humours to a part, are infinitely more frequent in the first than the
second class, because all these affections are essentially seated in
the capillary system, which is more developed in them.
Asphyxia, apoplexy, and all the affections that make the black blood
stagnate in the general capillary system, prove the same thing; in
fact, examine the livid head of one who has died of asphyxia, or of
apoplexy, you will see that it is especially in the skin and the
cellular texture that the blood is arrested; that the muscles, the
aponeuroses, exhibit besides the blood ordinarily found in them, only a
small quantity of superabundant fluid, in comparison with what there is
in the first organs.
_Remarks upon Injections._
From all that has been said, it is evident, that fine injections,
which form a convenient method of knowing the capillary system of an
organ, cannot show which vessels of this system admit red blood, and
which circulate only white fluids. In fact, the injected matter passes
equally into each, and we cannot distinguish that, which in the living
body is very distinct.
In order to form a precise and accurate idea of the quantity of
blood that enters each of the organic systems during life, it is
indispensably necessary to dissect those systems during life. I shall
frequently have occasion in this work, to make this truth felt, which
appears to me to be of much importance in many respects. If a fine
injection but partially succeeds, it almost always shows vessels that
really exist, but which were not sanguineous during life. Even the
coarse injections of our dissecting rooms frequently exhibit these
phenomena, especially in the face, the neck, &c.; and much more so, if
the matter injected is very delicate, and managed with much address. I
cannot conceive why physiologists have always taken as an indication of
the blood vessels, the state of injected organs; by opening any part of
a living animal, they may clearly see how deceptive this method is.
Injections are of no advantage except in the great vessels, in which
the blood circulates in a mass by the influence of the heart; in the
capillaries, they do not reach the precise point that exists in nature.
I wish that in dissecting rooms, the pupils, after having dissected
the arteries and veins, would finish their labours upon the vessels
by the dissection of a living animal, for the purpose of seeing the
quantity of blood that each system has in its capillaries; this
knowledge is essential to the study of inflammations, fungous tumours,
&c. Anatomical cabinets in which preparations are kept, are of no use
in this respect; these preparations are more likely to deceive in
proportion as the injections have succeeded well.
III. _Of the proportions which exist in the Capillaries between the
Blood and the Fluids that differ from it._
In the organs in which the blood, or the white fluids differing from
it, alone enter, there can be no variety in the proportions; but the
varieties are frequent in those where these fluids enter at the same
time. In the serous, the dermoid, the mucous systems, &c. there are
sometimes more, sometimes less small vessels filled with blood; the
cheeks, of which I have spoken, are a remarkable example of this.
The least emotion, the slightest agitation, or a motion a little too
violent, accumulates, diminishes, and varies, in a thousand different
ways, the quantity of blood in them. The whole exterior of the skin
exhibits the same phenomenon, though less frequently. When this organ
is irritated or excited at any point, it immediately reddens; it
becomes white if it is compressed. Cold and heat uniformly produce
analogous varieties, when the change from one to the other is sudden.
All the mucous surfaces exhibit the same arrangement; see the glans in
the erection of coition, or in the flaccidity that succeeds it; the
difference in the quantity of the blood that this external membrane
contains, is very evident. Lay bare a serous surface; at first
white, soon there will be numerous red streaks. If we could see the
capillaries of the glands, I presume that we should find the quantity
of blood variable in these vessels, and that during the time that the
secreted fluids are poured out in abundance, their system would be
more copiously supplied than at any of the time when it furnishes the
materials of the secretions. Why are not the kidnies and the liver
subject to the same varieties in the quantity of their blood, as the
surface of the skin? When, by a violent motion, sweat pours out in
abundance, and the external surface of the body looks more red, does it
not indicate that the blood is there in a greater proportion?
There are two things to be distinguished, however, upon this subject;
it is only when the copious secretions arise from an increase of
life, that a greater afflux of blood is supposed to take place in the
glandular system. When this increased secretion proceeds from a want
of vital energy, the blood is not in greater quantity in the gland.
The same observation applies to exhalation; thus, in the above case,
in the commencement of fever, &c. more blood enters the skin; but when
the sweat arises from weakness, as in phthisis, &c. there is not this
accumulation of blood in the capillary system. But this deserves a
longer explanation.
_Different proportions of Blood in the Capillaries, according as the
Secretions and Exhalations are active or passive._
I call those exhalations and secretions active, which are preceded
and accompanied by an evident development of vital forces; and
those passive which exhibit an opposite phenomenon. If we examine
the phenomena of the animal economy, it will be easy to see this
distinction, which appears to me essential in diseases; now, in
whatever organ you study it, you will always see every active
exhalation or secretion preceded by a greater afflux of blood to the
part; all passive exhalations and secretions present an opposite
phenomenon. Let us begin with exhalations.
1st. Cutaneous exhalation is active from violent running, or a paroxysm
of fever, as I have said, from the action of caloric upon the body,
hard work, &c.; the skin is then more expanded and deeper coloured;
more blood enters it, &c. This excitement of the skin makes it more
fit to be influenced by external agents, and to influence in its turn
all the other organs. It is the suppression of these transpirations
which causes so many accidents in the animal economy. Observe, on the
contrary, the complexion of the body in phthisical sweats, in those
produced by internal suppurations, in those that are the effect of
fear, in all those that are called colliquative, &c.; this complexion
is more pale than in a natural state; it is not capable of being
influenced, because its vital activity is then small, and its forces
languish.
2d. In the exhalations of the serous surfaces, there are some that are
essentially active; such is that of pus; for we shall see that the
formation of this fluid upon these membranes is without any kind of
erosion, that it flows evidently from the exhalants, instead of serum;
very often even it flows at the same time. Nothing is more frequent, in
fact, than the milky or purulent serum that is found in the peritoneum,
the pleura, &c. whether the fluids are exactly mixed, or the pus
floats in flakes in the serum. Now this active exhalation of serum or
of pus, which appears to be here principally coagulated albumen, this
exhalation, I say, is evidently preceded by a considerable accumulation
of blood in the capillary system, an accumulation which constitutes
inflammation, and without which exhalation cannot take place. Observe,
on the contrary, serous exhalation, increased by the weakness that any
organic disease gives to the serous membranes; to furnish this fluid,
the blood is never accumulated in them in greater quantity. Open the
membranous sacs, after the diseases of the heart, the womb, the lungs,
the liver, the spleen, &c. you will find them full of water, but more
diaphanous than usual, because they have received less blood.
3d. What I have said of the serous exhalations, must be said of the
cellular; some of them are active, such as those of pus and the
serum that sometimes accompanies it; others are passive, as the
leucophlegmasia after organic diseases. The same observation is to be
made as before; there is an accumulation of blood in the capillary
system in the first kind, a diminution of this fluid in the second.
Observe the fatty exhalation; a man in health who is very fat, has a
rosy colour upon the integuments distended with fat, which indicates
the abundance of blood in the capillary system. On the contrary, in
certain cases of sudden corpulency after diseases, in that which
is called false fat, and accompanies weakness, a general paleness
corresponding with the fatty bloating, indicates the absence of the
sanguineous fluid.
4th. Mucous exhalations present also an analogous phenomenon. I
shall prove soon that the hemorrhages from the mucous surfaces are
real exhalations; now some of them are active, a name which Pinel
has given them in his Nosography; these are the nasal, pulmonary,
gastric, uterine hemorrhages, &c. of young people and even of adults.
All these hemorrhages are accompanied by a local increase of action,
by greater heat, by a deeper colour of the mucous membrane, by the
greater abundance of blood in the capillary system. Who does not
know, that Galen predicted a hemorrhage from the redness which he
saw upon the nose and the eye of the patient? On the other hand,
observe the hemorrhages of the mucous surfaces, which take place
after long diseases, hemoptysis, which terminates the diseases of the
heart, hematemesis, the effect of organic derangement of the liver,
hemorrhages from the intestinal canal, so frequent at the end of all
the long organic diseases of the abdomen, &c. nasal hemorrhages in
certain low fevers, those which take place in scurvy from the different
mucous surfaces, the gums especially, &c. all these hemorrhages, which
are truly passive are not accompanied by this preliminary sanguineous
congestion in the capillaries, by this increased activity of vital
action; it might be said that it is the blood, which transudes, as
in the dead body, through the pores, that have not power to retain
it. This distinction is so true, that without making a theory of it,
physicians conform to it in their practice. We bleed to arrest an
active hemoptysis, but would you bleed to stop that which comes on in
the chronic diseases of the thorax? The same observation applies to
all the hemorrhages; they require means wholly opposite, according as
they are active or passive; a remark moreover that is applicable to
all diseases that have increased exhalations or secretions, whatever
may be their seat. It is not the phenomenon that we are to resist, but
the cause that has produced it. We diminish the forces, when serum is
accumulated in the thorax, from a pleurisy; we increase them, when it
accumulates from a disease of the heart, the lungs, &c.
What I have just said of exhalations applies to secretions. The mucous
glands pour out a greater quantity of fluids in two ways, sometimes
from irritation, sometimes from the want of force. When this happens
in the intestines, there results from it in the first case a diarrhœa
from irritation, in the second a colliquative one. Now it appears
that the blood enters the gland in greater abundance in the one than
the other case. Its increase takes place undoubtedly in most acute
catarrhs, in which there is active secretion of mucus; its diminution
or at least its want of increase is not less sensible in many chronic
catarrhs, in which we may consider the secretion as passive. We know
that the abundance of urine, of bile, sometimes supposes an increased,
sometimes a diminished action of the kidney and the liver. Is there not
a superabundance of semen from excess of vitality, and an unnatural
flow from weakness? All the secreted fluids have the same arrangement;
now according to these two opposite causes of the superabundance of
the secreted fluids, the capillary system of the glands is certainly
penetrated with a different quantity of blood. Though the phenomenon
be the same, the treatment in the diseases in which it is manifest,
is as in the preceding cases, wholly opposite, according as the local
increase or diminution of life concurs to produce it.
_Consequences of the preceding Remarks._
From all that I have said, it is evident that in the organs whose
capillary system contains in part blood, and in part different fluids,
the proportion of the first to the others is infinitely variable; that
a thousand causes in a state of health, as in that of disease, by
bringing to the organ more or less blood, can fill more or less its
capillary system.
The trunks and branches that go to an organ, are they more or less
dilated, according as the capillary system of this organ is more or
less filled with blood? For example, when the mucous glands pour out
fluid in the greatest quantity, are the neighbouring branches more
full? Some experiments that I shall mention hereafter do not seem to
prove it.