From the appearances noticed in the healthy intestine soon after death, it may be doubted, indeed, whether even this last phrase is quite specific enough ;—whether we ought not to regard* contraction itself (rather than an ab stract " contractility") as the inherent pro perty of the living organic muscle. In the observations just mentioned, we have seen that the death of the animal was soon fol lowed by an irregular, but distinct, contrac tion of the unstriped muscular coat of its in testine :— a contraction which was apparently excited by the air, but was certainly indepen dent of the nervous centres. This remained for a time, and then disappeared, never to return. Hence it seemed, in short, " a kind of precipitate rigor mortis, hastened by expo sure to the air." The truth of this analogy between the un striped and the striped muscle is confirmed by observations made on corpses in which all ex posure of the intestine has been avoided until an hour or two after death. A comparison of such examinations would show that the death of the intestine, like that of the ar teries, is accompanied by the access of a definite rigor mortis, which is closely analogous to the stiffening seen in the voluntary muscles. Both the access and disappearance of this contraction are, however, more rapid than in the striped fibres of the proper organs of locomotion. And its appearances are much less distinct. In the intestinal canal, it is chiefly recognized as a narrowing of the tube; which is attended by an increased thickness of its walls. But it is sometimes better evi denced by intus.susception of the canal; or by irregular contractions of its calibre.
But whatever the exact relation which the various contractions producible in the intes tine bear to the specific structure that forms its muscular wall, it seems certain that the true propulsive peristalsis of the healthy living ani mal is a complex and co-ordinate act, which is at least indirectly dependent upon the cerebro spinal centre. And \Veber's experiments on the highly excitable intestine of the Tench point definitely to the medulla oblongata, as that segment of the nervous centre by which this connection is chiefly brought about. While, as might have been expected, numerous observations concur to represent the pneumo gastric and splanchnic nerves as the channels by which this central organ influences the alimentary canal. But the exact degree in which the various vertebral and prever tebral centres of the sympathetic can trans mit, modify, or originate the nervous changes which pass to and from the bowel, is at present utterly unknown. There are how ever various reasons for suspecting, that neither of the two main ganglia which inter vene between any part of the intestinal sur face and the cerebro-spinal centre, really limit the transmission of an afferent, or give origin to an efferent, change.
Anti-peristalsis. —The ordinary theory of intestinal anti-peristalsis may be thus stated. At a certain stage of an intestinal obstruc tion, the immoderate irritation which it implies reverses the natural peristalsis of the bo% el ; so that, instead of proceeding towards the anus, it passes in the contrary direction. In
this way it impels the contents of the tube towards the stomach; whence they are vo mited by the aid of an extension or reproduc tion of the same action.
About eight years ago, the author f was led to. investigate this doctrine, until then uni versally accepted. He was thus led to the conviction, that it ought to be uncondition ally rejected ; that it was probably I.:Ilse ; and certainly had never been proved to be true. The following were his chief reasons for coming to such a conclusion :— 1. It is difficult even to conjecture any thing in the degree or kind of irritation pre sent in intestinal obstruction, which should limit the occurrence of anti-peristalsis to this state. 2. Since the physical state of occlu sion is the necessary condition of fmcal vorniting, it is probable that the causa tive process by which this occurrence is brought about must be physical also. 3. No anti-peristalsis has ever been observed; — the movements which occur in the obstructed bowel after death being similar in their nature to those witnessed in the healthy intestine under similar circumstances. 4. The whole of the appearances seen after death in the obstructed bowel, show that its contents have been pro pelled forwards towards the occlusion, and not backwards from it. 5. Distention of almost all the interval between the pylorus and the occluded part appears to be a condition of &cal vomiting ;—so much so, that the date of access of this symptom roughly indicates the locality of the obstruction.
Hence, instead of an imaginary anti-peri stalsis, the author ventured to propose a theory which seemed to deduce the process of fmcal vomiting from the ascertained conditions of its occurrence.
The complete obstruction of the intestinal tube at any point, gives rise to an accumu lation of its contents above the seat of the structure. This gradual distention of the bowel is accompanied by an active propulsion, which may often be seen and felt through the wall of the belly, as a violent writhing peristalsis. After a variable period, vomiting either occurs for the first time, or if already present from other causes, it becomes fmcal. But peristalsis in an obstructed tube dis tended with fluid, not only implies a forward movement in the particles that occupy' its peri phery, but also necessitates more or less of a backward current in those s; hich are situated in the axis or centre of the canal. And the uniform consistence of the distending fluid, or the return of solid fmces, through many feet of tortuous bowel,into the upper part of the canal, constitute frequent phenomena, which are best explained by the mixture and circulation that these two currents must tend to establish. On the fmcal fluid reaching the stomach, vo miting is excited. And it is scarcely neces sary to add, that this latter process, as usual, involves the more or less complete evacuation not only of the stomach, but also of the upper part of the distended small intestine.