Physiological Researches on Life and Death

by Xavier Bichat

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.