Until lately, it has been usual to augur the movements which occur during life, from an inspection of the intestines of healthy animals immediately after their death. On laying open the abdomen of a newly-killed animal, its intestines are seen lying perfectly still. But in a short time, those parts of them which are exposed to the air begin to experience vigorous contractile movements. In many instances, these contractions are irregular and undefinable, and are hence rather " vermicular" than " peristaltic." But in other cases, they take on appearances of a forward or backward course, or sometimes of each of these direc tions alternately. Where transverse constric tion is marked, it almost always takes a di rection downwards, or towards the anus; and is preceded by a dilatation which stretches the intestine to the full length of its mesen tery. After a few minutes, the contraction of the intestines generally gives them a nodu lated or almost moniliform shape, and the movement gradually ceases. On uncovering portions of the canal hitherto concealed, all these appearances are repeated. The con tracted state remains for some hours, and filially again disappears.
Now the tranquillity of these portions of intestine previously to the admission of air, the irregular and diffuse nature of the con tractions themselves, the final result on the intestine, and the effect of uncovering fresh portions—all these circumstances together offer the strongest probability, that the move ments witnessed are due to the contact of the air. And hence, although it is interesting to notice that these contractions often assume the form of a peristalsis (that is, of a circular constriction which travels slowly in a direc tion towards the rectum), still they do not warrant any conclusions as to the nature or force of those definite movements which are doubtless executed by the intestines during life.
Nor are the movements which result from applying a local irritation to the bowel, under the same circumstances, much more uniform or conclusive. -Unless excited before the commencement of the vermicular movements, or towards their close, they are obviously liable to be confused with these ;— which, indeed, they closely resemble. Thus, when the surface of the bowel is irritated mechani cally, a mere local contraction is sometimes produced. In other instances, and especially when the duodenum is the part attacked, the contraction extends downwards, or even upwards, from the irritated point. Sometimes this diffused contraction occurs almost imme diately after the application of the stimulus ; sometimes only after the lapse of a consi derable interval of time. Sometimes, vvithout any repetition of the stimulus, such waves are repeated; with short intermissions, and of gradually diminishing strength. Sometimes,
instead of one continuous wave, a broken or interrupted one is produced ; — a condition which is chiefly seen in the small intestine. Similar contractions may also be excited by the mechanical or chemical irritation of the nerves which immediately supply the intes tines. But irritation of the mucous membrane has little or no effect. Direct galvanic stimu lation, by means of the rotary electro-magnetic apparatus, repeats maily of these appearances. On applying the approximated electrodes to a given point, a short interval precedes the occur rence of a local contraction : and this con traction endures after their removnl. In some animals, this local contraction is Avly propa gated onwards, for a variable distance, towards the rectum. This continuous movement may even be repeated without any fresh appli cation of the stimulus. But that more diffuse irritation which may be produced by stroking the intestine with the wires gives rise to none but local contractions. While galvanizing the nerves reproduces the lively, but general, movements above alluded to. And finally, whatever be the form of irritation, it ceases to have any effect, soon after the lapse of that period at which the vermicular movements usually cease. This departure of irritability may, however, be retarded by warmth, or by preventing the access of air. And the capacity for such movements may sometimes be re stored by returning the divided and dead intestine to the belly of the living animal. Finally, though the repeated irritation of any one part soon exhausts its contractility, still, after a short interval of repose, it is at least partially restored.
On mechanically irritating the exposed intestines of the living animal, very different results are obtained. Compressing them between the fingers produces a local con traction, which lasts some few minutes, and then disappears. Scratching their peritoneal surface usually gives rise to elevations, which are just as local as the preceding depressions. These elevations,—which seem to be due to relaxation of the outer or longitudinal mus cular layer,—are accompanied by contractions of the deeper transverse fibres. And the latter can still be excited, after all possibility of pro ducing the former has been destroyed by cold. Mechanical or chemical irritation of the mucous membrane, or pinching or section of the nerves, produces no movements what ever :—even where the degree of nervous sti mulation is such as to cause convulsive move ments of the hind feet of the animal. And distention of the bowel with water seems to be equally inefficacious; indeed, it appears to leave the ordinary irritability by local stimuli very little affected.