PERISTALTIC MOTION. The terms peristaltic (Gr. clasping and compressing) and ver micular (or worm-like) are applied•to the peculiar motion or action of the muscular coat of the intestines, by which the substances contained within it are regularly moved onward: This action of the intestines is readily seen on opening an animal (a dog, cat, or rabbit, for example) immediately after it has been killed; and in these circumstances it is perhaps exaggerated, from the stimulating action of the cold air; mid it may he shown in an abnormally active state, although not altered in character, by subjecting the exposed intestines to the influence of the eleetro-magnetic machine.
It appears, from the observations made by Brinton, Todd, and Bownian, and others, on recently killed animals, that the peristaltic motion commences at the pyloric third of the stomach (see DIUESTION, OILGANS OF,), whence successive waves of contraction and relaxation are propagated downwards throughout the whole length of the intestinal canal. • "In examining a portion of intestine at the moment of its contraction, we per ceive a dilatation above it as well as below it; the latter produced by the protrusion into it of the contents of the now contracted portion of intestine; the former by the relax ation of a previously contracted portion. The rapid succession of these contractions and relaxations gives to the movements of the intestines the appearance of the writhings of a worm, whence they are distinguished by the appellation vermicular."—Todd and Bowimin's Physieca Anatomy of Man, vol, ii, p. 23G. These movements can occasionally be observed during life in the human subject, indirectly, in eases of extreme attenuation of the abdominal walls, and directly in wounds of the abdomen, and during certain sur gical operations. There are differences of opinion as to the cause of the peristaltic action; thus Todd and Bowman assert that "the intestinal movements are partly due to the influence of the stimulus of distention upon the muscular tissue. and partly to the
reflex action of the ganglia of the intestinal portion of the sympathetic, stimulated by the contact of the intestinal contents with the mucous membrane;" while Carpenter maintains that "the intestinal tuba from the stomach to the rectum is not dependent upon the nervous centers either for its contractility or for its power of exercising it, but is enabled to propel its contents by its own inherent powers.
Numerous observations tend to show that this motion has a nearly definite veiccity in each individual. Most commonly the act of defecation takes place with perfect regu larity every 24 or (more rarely) every 12 hours, the quantity discharged being almost constant if the mode of living does not vary. lleberden (Commentarii, p 14) mentions a person who regularly bad a motion once a month, and (by way of contrast) another who had twelve motions every day during thirty years, and then seven every day for seven years, and rather grew fat than otherwise. Pontetut ((Earns Posthumes, tome i. p. 27) records the case of a young lady who had no stool for upward; of eight years. althouglt during, the last year she ate abundantly of fruit, and drank coffee, milk. and tea, and Von' with yell; of eggs; but she had copious greasy sweats. Suclia case as this is possible, hut far from probable.
That the influence of expectant attention on the muscular movements of the intestine (and especially of its lower portion) is very great is shown in various ways. It is, for the most part, thus that 1:///0 operates in producing a readiness for defecation at one special hour in the day, ;Ind that bread-pills and other equidl j inert substances net on the bowels, if the patient believes them to be purgiitives. Dr. Carpenter, in his remarks on "the influence of expectant attention on mrtscuktr .movements." in the clintuer of his Haman PLygiology treating, "of muscular movements," mentions two very striking cases of the kind wvhich have fallen within his own knowledge.