Chapter VII (2)

[22] So, as long as the fluid is retained in the artery, which is
easily done by means of ligatures, no pain is manifested; but when
the irritating substance is carried by the vessels to the heart or
to any other sensible part, we can easily conceive that the animal
must experience pain, for the irritant always produces its effect,
whether it be carried directly to the part or arrive there by means
of the circulation.

[23] These expressions _dose_, _sum_, _quantity_ of sensibility
are incorrect, inasmuch as they exhibit this vital faculty under
the same point of view as the physical forces, as attraction,
for example; and as they present it to us as susceptible of
calculation, &c.; but, from a want of words for one science, it is
necessary, in order to make it understood, to borrow them from the
other sciences. There are expressions, like the words to _solder_,
to _glue_, to _unglue_, &c. that are used for the want of others in
the osseous system, and which really give very inaccurate ideas,
unless the mind corrects the sense.

[24] If the urine, during a perfect erection, does not go out
of the bladder, it is because the contraction of the muscles of
the perineum, and especially of the levator ani, prevents it. If
these muscles are relaxed, though the turgescence of the corpus
cavernosum and of the urethra remains the same, the urine flows out
without any other obstacle than what arises from the contraction of
the canal produced by the swelling of its parietes.

[25] These different excretory ducts do not exhibit in the mammalia
any contractility. There is no stimulus which can produce it in
them; I have tried them all in vain. In birds, on the contrary,
the ureters and the pancreatic and biliary canals are contractile,
and their motions, which return at intervals, are too well marked
to be mistaken. It appears that the contractility of the excretory
canals in the abdomen, is connected in these animals with the
absence of the diaphragm. We know in fact that this muscle in the
mammalia, assists by the pressure which it exerts, the course
of the secreted fluids, and renders useless the existence of
a peculiar motion in the canals which contain them. If it be
however pretended that this motion exists in them, but that it is
insensible, it must be allowed then, that it cannot perform the
office which is attributed to it, viz. that of obliterating an
opening often large enough to admit a quill. It is true, that if
the orifice of one of these canals be irritated for a long time, a
swelling of the membrane which lines it is sometimes produced, and
the opening is then really lessened. But in these cases there is
no occasion to be deceived; we see that this swelling is produced
at that point by the afflux of the fluids, as it would be in any
other part subjected to a similar excitement. Besides, it should
be observed that the obliquity of insertion of the excretory ducts
is alone sufficient to explain how the substances which pass in
front of their orifices are not introduced into them. In fact
these substances, at the moment of their passage, by the pressure
which they exert, tend to obliterate the opening of the canal,
by flattening its parietes against each other; it is thus that
the pressure of the urine, upon the inferior extremity of the
ureters, prevents this fluid from ascending towards the kidney. The
obliteration of the opening is but an accidental thing, and most
often is not even complete.

[26] It is not surprising, that a canal usually filled with the
excreted fluids should refuse to admit another which runs in an
opposite direction.

[27] All that is here said of the sensibility of the lymphatic
vessels, which makes them sometimes admit and sometimes reject
the effused fluids, is the more hypothetical, as it is not as yet
proved that these vessels are the agents of absorption. It should
be remarked, that the fluids that are supposed to be absorbed by
them, differ essentially in their chemical composition, from the
fluid that is usually found in their cavity. This fluid besides
varies but very little in its composition, though its appearance
is not uniformly the same; now, if it were the result of the
absorption of fluids differing from each other, its composition
ought also to vary as that of the chyle does, according to the
nature of the aliments.

Before the lymphatic vessels were known, the principal phenomena
of absorption were observed, and it was natural to attribute them
to the action of the veins. This opinion was maintained for a long
time after the discovery of the lymphatics. Finally, towards the
middle of the last century, Hunter being engaged in examining these
vessels, which he has done more to make known than any other man,
thought that they should be considered as the agents of absorption,
and this opinion was soon generally admitted. If we look for the
means by which he overthrew the ancient theory, we are astonished
to find that it was by five experiments only. Harvey did not with
equal facility obtain the acknowledgment of the circulation, and
perhaps there does not exist a second example of an opinion, which
was for a long time established, being abandoned so readily. It
should be remarked, that physiologists had not yet recovered from
the surprise produced by the discovery of a system of vessels so
extensive, and yet for so long a time unknown; they were impatient
to know the use of them; the veins had already the function of
returning to the heart the blood brought by the arteries; they
thought it would not impoverish them too much to deprive them of
the faculty of absorbing, in order to enrich the lymphatics with
it. Of the five experiments of Hunter, two are designed to prove
that the veins do not absorb, the object of the other three is to
show that the lymphatics do.

In the first experiment he injected tepid water into a portion of
intestine, and the blood which returned by the vein appeared to be
neither more diluted nor lighter than before. We cannot conceive
how by mere inspection, it is possible to judge if the blood
contains a certain quantity of absorbed water, a quantity which
must be proportionably very small, if we consider the whole amount
of blood that passes through the mesentric veins during the period
necessary for the absorption of the fluid. Hunter in the same
experiment tied the artery which went to the portion of intestine,
and examined the state of the vein. It did not swell, and its blood
did not become aqueous. But after this ligature, did the absorption
continue to go on in this portion of intestine, which still had no
doubt lymphatic vessels? This the author does not say. How moreover
should he think that the vein could continue its action when the
artery was tied?

In the second experiment Hunter injected milk into a portion of
intestine, and was unable to discover this fluid in the blood of
the mesentric veins; but at the period in which this experiment
was made, mankind were very far from being able to detect in the
blood a very small quantity of milk, and at the present day, with
all the aid derived from chemistry, we can hardly discover in
it a small quantity which is mixed directly with it. These two
experiments prove then nothing against the absorption of the veins;
as to those which he brings forward in favour of absorption by the
lymphatics, they are not more conclusive. I shall content myself
with relating one of them. He injected, into a portion of intestine
that was empty, a certain quantity of warm milk, and confined it
there by two ligatures. The veins that came from this portion were
emptied of their blood by several punctures made in their trunk.
The corresponding arteries were tied. He then returned the parts
into the abdomen, and drew them out again in half an hour. Having
examined them with attention, he observed that the veins were
almost empty, and that they contained no white fluid, whilst the
lacteals were almost full of it. But was not this white fluid that
filled them chyle rather than milk? Was it not there before the
injection of this liquid? In order to ascertain what takes place in
the lymphatic vessels during absorption, we must begin by examining
the state of these vessels before the experiment. But this is what
Hunter did not do, and it is this that renders his experiment of
no value. It is not very astonishing that he mistook the chyle
for the milk, since milk has for a long time been mistaken for
chyle. Flandrin, Professor of the Veterinary School at Alfort, has
several times repeated this experiment of Hunter; but he took care
before the injection of the milk to ascertain that the lymphatics
contained no white fluid; and he never found any in their cavity
after the experiment. I have myself many times performed this
experiment, with the same precaution, and I have uniformly obtained
the same results as those of Flandrin.

It would occupy too much time to examine all the reasons that have
been advanced for and against the absorption of the lymphatics; I
shall only relate some experiments I have made myself; but I ought
first to observe, that absorption undoubtedly takes place in parts
such as the eye, the brain, and the placenta in which the most
minute dissection has been unable to discover any lymphatic vessel.

_First experiment._--Four ounces of the decoction of rhubarb was
given to a dog, in half an hour after he was killed, and it was
found that more than half of the liquid had disappeared; the urine
evidently contained rhubarb, but the lymph in the thoracic duct
exhibited no trace of it.

_Second experiment._--A dog swallowed several ounces of alcohol
diluted with water; at the end of a quarter of an hour, the blood
of the animal had a very distinct odour of alcohol, but there was
nothing of the kind in the lymph.

Flandrin made a similar experiment on a horse, to whom he gave half
a pound of assafetida mixed with an equal quantity of honey. Six
hours after, the horse was killed. The odour of the assafetida was
very perceptible in the blood of the veins of the stomach, of the
small intestines and the cœcum; but it could not be perceived in
the lymph.

_Third experiment._--A dog was made to swallow six ounces of a
solution of Prussiate of Potash in water. In a quarter of an hour,
the urine very evidently contained some of the Prussiate; but the
lymph taken from the thoracic duct showed no appearance of it.

_Fourth experiment._--I gave to a dog, in whom I had tied the
thoracic duct, two ounces of a decoction of nux vomica. The effects
of absorption were as rapid as if the duct had been open. After the
death of the animal I satisfied myself, that the duct had been well
tied, and that there was no other branch, as there sometimes is, by
which the lymph could get to the subclavian vein.

I have varied this experiment by putting the poisonous fluid, into
the rectum, the sacs of the pleura and peritoneum. The results have
been uniformly the same.

_Fifth experiment._--M. Delille and myself made an incision into
the abdominal parietes of a dog, who had been fed very heartily
some hours before, so that the lacteals might be easily seen, and
we then drew out a portion of the small intestine upon which we
applied two ligatures three inches from each other. The lymphatics
that went from this portion of intestine were full of chyle and
very distinct. They were all tied and cut. The blood vessels were
also tied and cut, with the exception of an artery and a vein;
the portion of intestine also was cut off beyond the ligatures,
and thus it had no communication with the rest of the animal
except by the vein and artery which were left. These two vessels
were dissected with the greatest care, and even stripped of their
cellular coat, lest there might be some lymphatics concealed in
it; we then injected into the cavity of this portion of intestine
a decoction of nux vomica, and we retained it there by means of a
new ligature. This portion of intestine, covered with fine linen,
was restored to the abdomen; six minutes after, the effects of the
poison were manifested with their usual intensity.

_Sixth experiment._--M. Delille and myself separated the thigh of a
dog from his body, leaving only the crural artery and vein, which
kept up the communication between the two parts. These two vessels
were dissected with care, insulated to an extent of from two to
three inches, and even stripped of their cellular coat, for fear
it might conceal some small lymphatic vessel. Two grains of a very
active poison (the upas) were then inserted into the paw, and the
effects were as sudden and as intense as if the thigh had not been
separated from the body.

As it might be objected, that notwithstanding all the precautions
taken, the parietes of the artery or vein might still contain
some lymphatic, we varied our experiment so as to leave no doubt
on this point. The artery was cut entirely off, the communication
was reestablished between the two ends, by means of a leaden tube
introduced into their cavity, and fixed by proper ligatures.
The same was done for the vein. Thus there was no longer any
communication between the thigh and the rest of the body, except by
the arterial blood which came to the thigh, and by the venous blood
which returned to the trunk: the poison afterwards introduced into
the paw produced its effects in the ordinary time, that is in about
four minutes.

From these different experiments, it is right to conclude that the
minute branches of the veins possess the power of absorbing; that
they exert it on the surface of the mucous and serous membranes,
and in the interior of the organs; that the experiments that have
been quoted in favour of the absorption of the lymphatics are
inaccurate or incorrectly understood, and finally that there is no
proof that these vessels absorb any thing but chyle.

Is it now necessary to refer to the venous branches this
sensibility that has been attributed to the ultimate ramifications
of the lymphatics? But this sensibility, as we have already said,
would be constantly in error; the absorbent vessel does not select
one fluid in preference to another; all are indiscriminately
absorbed, even the most irritating, those in fact whose action is
sufficiently powerful to destroy the vascular parietes. Besides,
the phenomenon then continues, when it is no longer possible to
suppose the existence of this sensibility. After death even, the
venous branches absorb still as they do during life, if they are
placed in analogous circumstances; and to do this it is evident,
that an internal current must be established, which resembles the
course of the blood. I shall now relate an experiment, which I made
on this subject, and which I selected from many others, because it
appeared to me to be very conclusive.

I took the heart of a dog that had died the day before; I injected
into one of the coronary arteries some water of the temperature
of 30 degrees of the centigrade thermometer. This water returned
easily by the coronary vein to the right auricle, whence it flowed
into a vessel or dish. I poured half an ounce of slightly acid
water into the pericardium. At first the injected water exhibited
no sign of acidity; but in five or six minutes it presented
unequivocal marks of it.

Absorption then can take place without the assistance of this
sensibility, as well as of this insensible organic mobility, which
is supposed to be in the ultimate vascular extremities, in the
absorbing mouths, as they are called. But do these mouths really
exist? Do the last capillary branches terminate abruptly with a
large opening on the surface of the membranes or in the texture of
the organs? Can the absorbed fluids pass through their parietes as
oxygen does in the lungs to arrive at the blood which it modifies?
We are unable to make experiments on these small vessels, that
are not cognizable by our senses; let us make them on the large
ones, and if they permit fluids, in which they are immersed, to
pass through them, for a stronger reason we may suppose that it
takes place in the capillaries, whose parietes are so much more
delicate and consequently more permeable. Now we have confirmed by
experiments what we had suspected; the first attempts were made on
dead vessels.

I took a portion of the external jugular vein of a dog; I stripped
it of the surrounding cellular texture; I attached to each of its
extremities a glass tube by means of which I established a current
of warm water through its interior; I then immersed the vein into a
liquor slightly acid.

It is seen by the arrangement of the apparatus that there could not
be any communication between the internal current of warm water and
the external acid liquor.

During the first minutes the liquid that I collected did not
change its nature; but after five or six minutes the water became
perceptibly acid; absorption had taken place.

The same experiment was repeated on veins taken from human
subjects; the effect was the same; it was the same also with the
arteries, but a little slower from the greater thickness of their
coats.

It remained to be seen if in a living animal absorption thus took
place through the parietes of a large vessel. I know that the
textures that were permeable after death, are almost all so during
life, though the contrary is generally believed. If we inject
into the pleura of a living animal a certain quantity of ink, at
the end of an hour, and often sooner, we shall find the pleura,
the pericardium, the intercostal muscles, and the surface of the
heart itself, evidently of a black colour. It is true that the
signs of this exudation are not always apparent. Thus after death,
the transudation of the gall bladder is rendered evident by the
colouring of the neighbouring parts. During life, on the contrary,
as fast as the colouring particles are deposited, they are absorbed
by the serous membrane which covers the surrounding parts, and
carried off by the sanguineous current which runs through this
membrane and the subjacent organs.

From these considerations we must believe that absorption may take
place through the parietes of the vessel during life as after
death. To be satisfied of this I made the following experiment:

I took a young dog of about six weeks old. At this age the vascular
parietes are delicate, and consequently more likely to render
the experiment successful. I laid bare one of the jugular veins;
I insulated it perfectly in its whole length; I stripped off
carefully every thing which covered it, and especially the cellular
texture and some small vessels that ramified on it; I placed it
on a card, that it might not be in contact with the surrounding
parts; I then let fall, on its surface and opposite the middle of
the card, a thick aqueous solution of an alcoholic extract of nux
vomica, a substance the action of which is very powerful on dogs;
I took care that none of the poison could touch any thing but the
vein and the card, and that the course of blood was free in the
interior of the vessel. Before the fourth minute, the effects that
I expected appeared, at first feeble, but afterwards with so much
power as to render inflation of the lungs necessary to prevent the
death of the animal. I repeated this experiment on an adult animal
of a much larger size than the preceding one; the same effects
appeared but slower, on account of the greater thickness of the
parietes; they began to appear in fact after the tenth minute.

After satisfying myself with this result respecting the veins,
I thought I would ascertain if the arteries exhibited analogous
properties. These vessels are in a less favourable condition;
their texture is less spongy than that of the veins and with an
equal caliber, their parietes are much thicker. It was easy then
to foresee, that if the phenomenon of absorption showed itself, it
would appear much slower than in the veins; this was confirmed in
an experiment on two large rabbits, in whom I dissected perfectly
clean one of the carotid arteries. It was more than a quarter
of an hour before the solution of nux vomica passed through the
parietes of the artery. As soon as I saw the symptoms of poisoning
distinctly, I stopped moistening the vessel; yet one of the rabbits
died. In order then to convince myself that the poison had really
passed through the arterial parietes, and that it had not been
absorbed by small veins which might have escaped my dissection, I
carefully detached the vessel that had been used in the experiment;
I cut it open in its whole extent, and I made those who assisted
me taste a little of the blood, that was still adhering to the
internal surface; they all perceived in it, and I did myself, the
extreme bitterness of the extract of the nux vomica.

To these experiments may be objected a fact that is observed,
which is, that absorption does not take place the same under all
circumstances; its activity is redoubled or diminished, according
to the state of some other functions. Thus during a paroxysm of
fever, a medicine, which would usually act with great effect, often
produces, when given in a double or treble dose, no perceptible
effect. Now if absorption, was a purely mechanical phenomenon,
would it undergo modifications in relation with those of the vital
functions? Without doubt it would; for these modifications of the
functions may introduce new physical circumstances favourable or
injurious to the production of a mechanical phenomenon. Thus in the
present case, the state of fever, by accelerating the circulation
distends with blood the arteries and the veins. The fluid that is
to be absorbed must pass from the exterior to the interior of these
vessels. Now it may be easily conceived, that the quantity of blood
which they contain must have a great influence upon the production
of the phenomenon by the greater or less degree of tension of their
parietes. This is moreover completely confirmed by experiment.

We can, without producing a very great disturbance in the
functions, increase at pleasure the quantity of fluid which passes
through the blood-vessels, by carefully injecting into the veins
water the temperature of which is near that of the blood. An
artificial plethora is thus produced, followed by very curious
phenomena, of which I shall have occasion hereafter to speak. One
day while making this experiment, the idea occurred to me of seeing
what influence the plethora thus produced would exert upon the
phenomenon of absorption.

In consequence, after having injected into the veins of a dog of
middle size about a quart of water, I placed in the pleura a small
dose of a substance, the effects of which were well known to me.
These effects did not show themselves till many minutes after
the period in which they usually appear. I soon made the same
experiment on another animal with the same result.

In many other trials the effects showed themselves at the period in
which they ought to have appeared; but they were evidently weaker
and prolonged much beyond the ordinary time.

Finally, in another experiment in which I had introduced as much
water as the animal could bear and live, the effects did not appear
at all. I waited nearly half an hour for effects which commonly
show themselves in two or three minutes. Presuming then that the
distension of the vessels prevented the absorption, I endeavoured
to satisfy myself of it, by seeing if after the distension had
ceased, absorption would be any longer prevented. In consequence,
I bled the animal copiously from the jugular, and I saw, with the
greatest satisfaction, the effects appearing as the blood flowed
out.

It was proper to make the opposite experiment, that is to say to
diminish the quantity of blood, in order to see if absorption would
take place sooner. This took place in fact, as I thought it would;
about half a pound of blood was taken from an animal; the effects,
which did not usually appear till after the second minute, showed
themselves in thirty seconds.

Yet it might still be suspected, that it was less the distension of
the blood-vessels than the change of the nature of the blood that
opposed absorption. To remove this difficulty I made the following
experiment; a dog was bled copiously; the place of the blood which
he had lost was supplied by water at the temperature of 40 degrees
of the centigrade thermometer, and a certain quantity of a solution
of nux vomica was introduced into the pleura. The consequences of
it were as prompt and as powerful, as if the nature of the blood
had not been changed; it was then to the distension of the vessels
that must be attributed the want or diminution of absorption.

The consequences that may be deduced from the experiments I have
just related will acquire new force, if we connect with these facts
a multitude of pathological ones, which are every day seen; such as
the cure of dropsies, engorgements and inflammations by bleeding;
the evident want of action of medicines at the moment of a violent
fever, when the vascular system is powerfully distended; the
practice of certain physicians who purge and bleed their patients
before administering active medicines to them; the employment of
cinchona at the period of remission for the cure of intermittent
fevers; general or partial oedema from organic disease of the heart
or lungs, and the application of a ligature upon the extremities
after a puncture or a bite of a venomous animal, to prevent the
deleterious effects which are the consequence of it.

On the whole, I think, it may be concluded from the preceding
experiments that the capillary attraction of the small vessels is
one of the principal causes of the absorption called venous. If the
lymphatics do not appear to enjoy in the same manner the faculty of
absorption, it probably arises not from the nature of the parietes,
the physical properties of which are nearly the same as those of
the veins, but from the want of a continuous current in their
interior.

In this note I have brought together the absorption of the gases
and that of fluids. This resemblance holds only as it relates to
the permeability of the textures by these two orders of bodies. As
to the cause of the absorption of the two, it cannot be the same,
since gases are not subjected to capillary attraction.[28]

[28] _Note by the Translator of Magendie’s Additions._--In the
preceding note M. Magendie has not done justice to Mr. Hunter.
Without entering at all into the examination of the question,
whether absorption is performed by the lymphatics or the veins,
it is due to Mr. Hunter to contradict the assertion, that “he
overthrew the ancient theory by _five experiments only_.” He was
not a man who adopted his opinions loosely or on slight grounds,
and in the present case he performed between twenty and thirty
judicious and satisfactory experiments, in the presence of several
physicians and surgeons. It is true that these were performed on
five different animals only, but if the result were uniform, this
number was as good as five thousand or any other one that could be
named.

G. H.

(See Hunter’s Commentaries and Cruikshank on the Absorbents.)

[29] Those theories no doubt are very incomplete that are borrowed
from hydraulics, and probably will be so for a long time; but
it arises from this, that the science on which it is founded,
hydrodynamics, is still but little advanced. A great advance will
unquestionably be made in physiology, when we shall arrive at a
knowledge of the course of a fluid in a system of canals, which
have the same physical conditions as the system of arterial and
venous vessels. But it will be a long time before science will
have arrived at that point. Is it necessary for this to make no
use, in the explanation of the circulation, of the few facts which
are known upon the course of the fluids? Is it necessary to enter
entirely into the field of hypothesis, to suppose in the small
vessels a sensibility and a contractility which evidently do not
exist in the large ones? I cannot believe it, and I think even
that if this hypothesis should be true, and if there should be
demonstrated for the capillary vessels, those properties which are
attributed to them, and which would have an influence on the course
of the blood, we should then know but one of the conditions of this
very complicated problem, and this would not in any degree do away
the necessity of knowing all the mechanical conditions.

[30] Even in reasoning according to the hypothesis of Bichat, and
admitting the existence of this organic sensibility, it would
always be inaccurate to say, that the contraction is uniformly
in proportion to the sensation. How is it to be known in fact?
Since this sensibility is not transmitted to a common centre, it
might very well be excited without our being informed of it by any
apparent effect. Sometimes also a very evident contraction would
correspond to the slightest excitement.

[31] The contractility in the different organs in which we can
observe it does not exhibit characters so striking as those which
Bichat here assigns to it, and the motions which he ranks in
the same class have the greatest differences among them. To be
convinced how little justice there is in this division, it will
be sufficient to trace the progress of the food, along its whole
course, to the interior of the digestive canal. The first act
which is presented to our observation is entirely voluntary; this
is mastication; the act which follows it is not so completely so.
Deglutition in fact can sometimes take place against the will, if a
body of a proper consistence is at the entrance of the pharynx. We
have but an imperfect control over the muscles of the uvula and the
velum palati, if we wish to move these parts separately; we have
perhaps less power still over the contraction of the muscles of the
pharynx, though they do not appear to differ from the locomotive
muscles, either in their symmetry, or in the arrangement and colour
of their fibres, or in the nerves which they receive; nor finally
do they differ in the sudden, instantaneous contraction, wholly
different from the slow contraction, the vermicular motion of the
stomach and intestines.

After having passed the pharynx, the alimentary mass enters the
œsophagus. The motions are there still under the influence of the
nerves; but they are not at all under the influence of the will.
The muscular layer which produces them has not the appearance,
the red colour of the voluntary muscles; but it still preserves
something of the sudden motion of their contraction. Hence we see,
that the motions of the œsophagus cannot be ranked either among the
motions of organic life, since they cease by the division of the
nerves, or among those of animal life, as they are not under the
influence of the will. It is remarkable also that Bichat, who, in
this and the following paragraph, announces the characters of the
different kinds of contractility, does not speak of the œsophagus,
whilst he offers as an example the motions of the bladder, the
heart, the stomach and the intestines.

When Bichat wrote this work, hardly any thing of the motions of
the œsophagus was known, except from the writings of Haller, who
made but four experiments on the subject. I wished to observe them
myself, and I have discovered many facts which I think interesting;
I shall relate them here as I described them in a memoir read to
the Institute in 1813. Before attempting to ascertain what part
the œsophagus took in the passage of the food, it was proper to
ascertain its state when it was supposed to be at rest. In the
first experiments, I noticed an important phenomenon, and which
hitherto had escaped the observation of physiologists, viz., that
the lower third of the œsophagus has constantly an alternate motion
of contraction and relaxation, which appears to be independent of
all foreign irritation. This motion appears to be confined to the
portion of the tube which is surrounded by the plexus of nerves of
the eighth pair, that is to say, to about its lower third; there is
no trace of it in the neck nor in the superior part of the thorax.
The contraction appears like a peristaltic motion, it begins at the
junction of the superior two thirds with the inferior third, and is
continued to the insertion of this tube in the stomach. When the
contraction is once produced, it continues for an uncertain time;
usually it is less than half an hour. The œsophagus contracted
in this way in its lower third is hard like a cord powerfully
stretched. Some persons whom I have made feel of it in this state
have compared it to a rod. When the contraction has lasted the time
I have just mentioned, the relaxation takes place suddenly and
simultaneously in each of the contracted fibres; in some cases,
however, the relaxation seems to take place from the superior
fibres towards the inferior ones. The œsophagus examined during
the state of relaxation exhibits a remarkable flaccidity, which
contrasts wonderfully with the state of contraction.

This alternate motion is dependent on the nerves of the eighth
pair. When these nerves are cut in an animal, this motion entirely
ceases; the œsophagus contracts no more, but it is not in a state
of relaxation; its fibres without the control of nervous influence
shorten; it is this which produces, so far as the touch is
concerned, an intermediate state between contraction and relaxation.

When the stomach is empty or half full of food, the contraction of
the œsophagus recurs at much longer intervals; but if the stomach
be powerfully distended by any cause, the contraction of the
œsophagus is usually very powerful, and continues for a much longer
time. I have seen it, in cases of this kind, continue more than ten
minutes; under the same circumstances, that is to say, when the
stomach is excessively full, the relaxation is always much shorter.

If during the time of contraction, we wished, by mechanical
pressure made on the stomach, to make a part of the aliments which
it contained pass into the œsophagus, it would be necessary, in
order to accomplish it, to employ a very considerable force; and
often even we should not succeed. It seems that pressure increases
the intensity of the contraction, and prolongs its duration. If, on
the contrary, the stomach is pressed during relaxation, it is very
easy to make the substances it contains pass into the cavity of the
œsophagus. If it be a liquid, the slightest pressure, sometimes
even its own weight, or the tendency which the stomach itself has
to contract, will bring about this result. When the stomach is laid
bare and distended above measure, fluid does not usually enter into
the œsophagus, because, as we have said, the distension of the
stomach is a cause which prolongs the contraction of the œsophagus.

The passage of a fluid in the œsophagus is usually followed by its
entrance into the stomach. Sometimes however the fluid is thrown
out. When it goes into the stomach, the œsophagus contracts nearly
the same as in deglutition, sometimes almost immediately after it
has entered it; at other times the œsophagus allows itself to be
considerably distended before it pushes it into the stomach.

It was at the moment of deglutition that Haller observed the
motions of the œsophagus, and the description which he has given
of them is very accurate for the two superior thirds of the canal;
but the action of the inferior third is essentially different;
and this distinction seems to have escaped him. Haller says that
the relaxation of each circular fibre immediately follows the
contraction; and this is true of the portion of the canal situated
in the neck and in the superior part of the thorax; but it is
not accurate for the inferior portion, in which we see that the
contraction of all the circular fibres is continued long after
the entrance of solids or fluids into the stomach. At this moment
the mucous membrane of the cardiac extremity of the œsophagus,
pushed by the contraction of the circular fibres, forms a very
considerable projection into the cavity of the stomach. The
contraction usually coincides with the period of inspiration, when
the stomach is more strongly compressed; the relaxation takes place
most often at the time of expiration. When the aliments have once
entered the stomach, it is this contraction of the inferior part
of the œsophagus which opposes their return. The resistance that
is offered at the other orifice is not of the same species. In
living animals, whether the stomach be empty or full, the pylorus
is uniformly shut by the contraction of its fibrous ring and the
contraction of its circular fibres. There is frequently seen in the
stomach another contraction, at one or two inches distance, which
appears to be designed to prevent the aliments from arriving at the
pylorus. We perceive also irregular contractions, beginning at the
duodenum, and extending to the pyloric portion of the stomach, the
effect of which is to push back the aliments towards the splenic
part.

The aliments remain in the stomach long enough to undergo no other
modifications than those which result from their mixture with the
perspiratory and mucous fluids, which are constantly found in it
and renewed there. During this time the stomach remains uniformly
distended; but afterwards the pyloric portion contracts in its
whole extent, especially in the part nearest the splenic portion,
towards which the aliments are carried. Then there is found, in the
pyloric portion, only the chyle mixed with some unchanged aliments.
When there is accumulated in this part a quantity of it, which is
never very considerable, there is seen, after a moment of rest, a
contraction at the extremity of the duodenum; the pylorus and the
pyloric portion soon take part in this motion, and the chyle is
forced towards the splenic portion; but afterwards the motion is in
an inverse direction. The pyloric portion, which allowed itself to
be distended, contracts from left to right, and directs the chyle
towards the duodenum, which soon passes the pylorus and enters the
intestine. The same phenomenon is repeated a certain number of
times, then it ceases, and commences again after some time. This
motion, when the stomach contains much food, is limited to that
part of the organ nearest the pylorus; but as it becomes empty, the
motion extends, and appears even in the splenic portion when the
stomach is almost entirely evacuated. In general, it becomes more
evident at the end of chylification.

The motion which produces the progression of the chyle in the
small intestines is very analogous to that of the pylorus; it is
irregular, made at variable intervals, it is sometimes in one
direction and sometimes in another, and sometimes appears in many
parts at once; it is always more or less slow, it produces changes
of relations in the intestinal circumvolutions, and it is entirely
beyond the influence of the will.

We should form a very false idea of the motions of the small
intestines during digestion, if we judged of them by those which
these intestines exhibit in an animal recently killed. In this
case, it is not the annular fibres only that enter into action,
so as to exhibit, by their successive contractions, a vermicular
motion. The longitudinal fibres act also in a very conspicuous
manner, and produce a rolling of the intestinal circumvolutions,
which change their relations at every instant. These motions are
never more evident than when the whole mass of intestines is
removed from a living animal.

The motions of the large intestines have nearly the same characters
as those of the small intestines, like these last, they are not
always in the same direction, but push the substances which
are contained in their cavity, sometimes towards the ileum and
sometimes towards the anus. But by means of this motion, these
substances which have already the character of _feces_, can never
re-enter the small intestines. The cause that prevents their
return is different from that which prevents the return into the
stomach of the substances contained in the duodenum. The obstacle
in this case, we have said, is produced by the contraction of
the contractile rings, which are found at the extremity of the
two cavities; in the other, it is produced by a cause purely
mechanical, by the arrangement of the ileo-cecal valve. Hence it
follows, that if the mode of contraction of the different parts
of the intestinal canal be perverted by any cause, it might
happen that their contraction towards the pylorus would not take
place when the duodenum was affected with its anti-peristaltic
motion, and then the substances contained in it, pushed by the
contraction of the annular fibres, would re-enter the stomach. At
the coecum, on the contrary, as the obstacle is purely mechanical,
so long as the ileo-cecal valve is not broken, it will present an
insurmountable obstacle to the return of the _feces_ into the small
intestines.

The motions of the large intestines, sufficient to carry the feces
into the rectum, would not, in a state of health, be powerful
enough to expel them entirely, by overcoming the resistance which
the sphincter constantly presents; in expelling the feces, the
contraction of the intestine is assisted by the pressure which
arises from the lowering of the diaphragm, and by the contraction
of the abdominal muscles.

We have just pointed out the motions which carry the alimentary
mass along the intestines. We may see that they have but little
resemblance among them. The only character that is common to them
is that of not being under the influence of the will. Yet there is
an exception to this in some individuals who possess the faculty
of ruminating. (The will is seen exerting itself on the production
of other _sensible organic motions_. Bayle could stop at will the
pulsation of his heart.) If we examine the motions of the digestive
tube when it is free of aliments, we see their difference in a
manner not less striking. The œsophagus exhibits those alternate
motions that we have described; a very powerful contraction of its
inferior third, and then suddenly the most complete relaxation.
In the stomach we see only some undulations, that go irregularly
from one orifice to another. In the intestines, these motions
exhibit nearly the same regularity, but the groove formed by the
contraction of the annular fibres is deeper, and the undulatory
motion is not so slow. If a stimulating medicine is introduced
into the stomach, these contractions become more evident, and the
motions more rapid; but they always preserve the same character.
The contraction takes place progressively, and never in the sudden
manner of a muscle of locomotion. Of all the substances which can
be used to ascertain these motions, there is no one whose action is
more efficacious than veratrine, a new vegetable alkali extracted
from the _veratrum sabadilla_. If the external parietes of the
digestive tube be excited by any stimulus, by touching it with the
finger, by a puncture, or by the galvanic fluid, there is in the
œsophagus a sudden contraction of the longitudinal and circular
fibres, which narrows the organ and shortens it at the same time;
the relaxation takes place instantaneously and in as striking a
manner. In the stomach, no motion is perceived in the direction of
its length; we see only an annular contraction, which is developed
slowly at the excited point, and which is usually not transmitted
to the neighbouring parts. In the intestines, the excitement
produces a very decided contraction, and very often in the
neighbouring parts a kind of peristaltic motion; but this motion is
always slow and does not at all resemble the sudden contraction of
the œsophagus.

The difference between the motions of the œsophagus and those of
the other parts of the intestinal canal is very remarkable in
birds. In them the œsophagus appears to be entirely membranous; and
yet it contracts like a muscle of locomotion; whilst the stomach,
which has red muscles very similar to the locomotive muscles, has
slow, gradual vermicular motions, like all the canal which is below
it.

There exists finally between the motions of the intestinal canal a
difference relative to the manner in which they terminate. Those
of the intestines, but little sensible during life, acquire at
the moment of death a very great intensity; whilst those of the
œsophagus, before so distinct, cease immediately, and in the most
complete manner.

[32] It is not the dartos that contracts in the motions of the
scrotum, it is the skin itself that produces that vermicular
motion that is observed in this part. This motion can be produced
by stimuli of very different kinds; by the impression of cold, by
pinching the skin or by fear. I have seen these motions so great
in a man on whom I was about to operate for hydrocele, that I was
obliged to wait for a long time for fear of wounding the testicle,
which, by those motions, ascended and descended precipitately.

[33] It might be thought from this expression, that Bichat supposed
that the great arteries influenced the course of the blood by an
active contraction analogous to the muscular contraction; but
this was not his opinion. He only wished to say, that the blood
continued to move in the great arteries solely by the influence of
the heart. This contraction of the great arterial trunks has been
heretofore maintained by many anatomists, and is even at present
by some. There are at the present day three principal theories
relative to the circulation.

In the first, it is contended that all the parts of the arterial
system are irritable, and that they contract like the muscular
texture; many even add that they can dilate spontaneously, as takes
place every instant in the heart. According to this supposition,
the arteries alone would be able to continue the course of the
blood.

In the second opinion, which is that of Harvey, and which is still
adopted, more particularly by the English physiologists, it is
affirmed on the contrary, that the arteries are not contractile
in any point; that if they do contract in certain cases, it is in
virtue of that property common to all the solids, by which they
return upon themselves, when the cause that has distended them
ceases to act. The partisans of this opinion conclude that the
arteries have not and cannot have any influence upon the motion
of the blood which runs through them, and that the heart is the
principal, and as it were, the sole agent of the circulation.

Finally the third opinion, that which now prevails most generally
in France, consists in a union of the two preceding ones; the
trunks and principal arterial branches are considered as incapable
of acting upon the blood; but this property is attributed to the
small arteries, and it is thought to be very great in the last
divisions of these vessels. Thus, in this mixed opinion, the blood
is carried by the sole influence of the heart in all the arteries
of a considerable size; it is moved in part by the influence of the
heart and in part by that of the parietes in the smaller arteries,
and finally it is moved by the sole action of the parietes in the
last arterial divisions. This action of the small vessels is also
described as the principal cause of the course of the blood in the
veins.

In a question of this nature our opinion should be determined by
experiments alone. This presents many points for elucidation.

The first and the easiest to be decided is to ascertain if the
arteries are or are not irritable. The problem was in some measure
resolved in relation to the great arteries by the experiments of
Haller and his disciples, by Bichat himself, and by those which M.
Nysten has made upon man. For the purpose of being more perfectly
convinced, I have sought, by all the known means, to develop
the irritability of the arterial parietes; I have successively
subjected them to the action of pricking instruments, of caustics
and of galvanism, and I have never perceived any thing which
resembled a phenomenon of irritability; and as those who maintain
the irritability of the arteries pretend that if we do not perceive
the contractions, it is because the experiments are made on too
small animals, in whom the effects are but slightly apparent in
consequence of the small diameter of these canals, I have repeated
the experiment on large animals, on horses and asses, and I have
never observed any other motions than the communicated motions.

As the great arteries show no contraction, we ought to believe
that the small ones would not; but as among the physiologists who
reject the irritability of the arterial trunks, some like Haller,
do not speak of the branches, others accord to them contractility,
it becomes necessary to test this question by experiment; now these
small vessels, like the larger ones, remain perfectly immoveable
under the action of the scalpel, caustics and a stream of galvanic
fluid.

Irritability does not exist then in the large or the small
arteries. Respecting the last arterial divisions, as the vessels
which form them are so small that they cannot come under the
cognizance of the senses, at least in a state of health, no one can
affirm or deny that they are irritable. Yet from analogy we ought
to conclude, that they have no sensible motion. In cold-blooded
animals, in fact, it is easy to see the blood circulating in
these vessels, and even passing into the veins; now the vessels
themselves appear to be completely immoveable.

As the arteries cannot act upon the blood by contracting in the
manner of muscles, must we conclude that they have no action
upon this fluid, and that they are in relation to it nearly like
inflexible canals? I am very far from thinking so. If in fact the
arteries had no influence upon the blood, this fluid, moved by
the sole impulse of the heart, would, from its incompressibility,
be alternately in motion and at rest. This is indeed what Bichat
thought, and what he has advanced in his other works; it is what
has been since maintained in a more formal manner by Dr. Johnson
of London. It is however very easy to prove that it is not in this
way that the blood is moved in these vessels. Open a large artery
in a living animal, and the blood will escape in a continuous jet,
but by jerks; open a small artery, and the blood will flow out in
a continuous and uniform jet. The same phenomena take place in
man if the arteries are opened, either by accident or in surgical
operations. The heart being unable to produce a continuous flow,
since its action is intermittent, it must be then that the arteries
act upon the blood; this action can only be the disposition
which they have to contract, and even to obliterate their cavity
entirely. Bichat thought that his tendency to narrowing was not
sufficient in the arteries to expel the blood contained in their
cavity. He maintains that the vessel does not contract upon itself
only when the blood has ceased to distend it. If it were so, the
arteries would be equivalent to inflexible canals, and the course
of the arterial blood would not be continuous; but we can easily
demonstrate that the force with which the arteries contract is more
than sufficient to drive out the blood that they contain.