INTUSSUSCEPTION OF THE SMALL INTESTINES. 763 
former it is necessary to have a clear conception of the 
peculiar vermicular movement of the intestines called the 
peristaltic action. Unless this is understood, it is difficult to 
conceive how invagination can take place. To assist, there¬ 
fore, the tyro in science, into whose hands these remarks may 
fall, and who may be only imperfectly acquainted with the 
way this function is performed, I will briefly describe it. 
The peristaltic action consists of alternate contractions 
and dilatations of successive parts of the intestinal tube, both 
being effected by its muscular or middle coat, which is com¬ 
posed of two orders of fibres, one taking a circular and the 
other a longitudinal direction. At any one point of the 
tube—say, for example, the anterior—the circular order may 
be in a relaxed and the other in a contracted condition, 
the bowel being in consequence dilated at this part. In 
this condition, having received some of the ingesta, the cir¬ 
cular fibres contract first anteriorly, then gradually onwards, 
pressing thereby the contained matter in a direction towards 
the anal opening; these fibres then relax and the others 
contract, the tube being thus dilated and ready to receive and 
grasp, as it were, a fresh supply of ingesta, which, in its turn, is 
likewise moved onwards in the same way. Thus, by a series 
of wave-like movements throughout the whole length of the 
intestinal canal, not only are the contents passed gradually 
onwards, but also all their component parts are exposed to 
the absorbing surface of the mucous membrane. Now, as 
the muscular coat of the alimentary tube is under the in¬ 
fluence of the nerves, so, if it be not unduly excited, the ver¬ 
micular motion goes on regularly, and without any pain or 
inconvenience; and as the action of this coat is alternate, so 
are we led to the conclusion that the supply of nerve force is or 
must be the same, at least in degree. But as these alterna¬ 
tions are in harmony with each other, no evil result will 
follow. If, however, on the other hand, the nerves sup¬ 
plying the intestine be unduly irritated as a whole, or even 
in places only, abnormal action will be the result. General 
increased action of the whole of the muscular coat of the in¬ 
testine may be induced by some disturbing cause, primarily 
affecting the ganglia from whence the nerves proceed ; or 
the peripheries of the nerves themselves, as distributed on 
the inner coat of the bowel, may be firstly excited, and thus 
affect, but by a more circuitous route, the muscular coat. The 
contents of the canal would thus be hurried onwards at a rate 
incompatible with health, and even diarrhoea maybe thereby 
produced. But I can conceive that this increased action of 
the muscular coat of the intestines may be partial, and, con- 
