268 INTESTINAL DIGESTION. 



the transverse fibres are thin and apparently of little power, their contraction 

 is undoubtedly sufficient to empty the sacculi, when assisted by the move- 

 ments of the longitudinal fibres, especially as the canal is never completely 

 filled and the faeces are frequently in the form of small, moulded lumps. By 

 these slow and gradual movements, the contents of the large intestine are 

 passed toward the sigmoid flexure of the colon, where they are arrested until 

 the period arrives for their final discharge. The time occupied in the pas- 

 sage of the faeces through the ascending, transverse and descending colon is 

 undoubtedly variable in different persons, as great variations are observed in 

 the intervals between, the acts of defalcation. During their passage along 

 the colon, the contents of the canal assume more and more of the normal 

 f aacal consistence and odor and become slightly coated with the mucous secre- 

 tion of the parts. 



The accumulation of faeces generally takes place in the sigmoid flexure of 

 the colon ; and under normal conditions, the rectum is found empty and 

 contracted. This part of the colon is much more movable than other por- 

 tions of the large intestine. At certain tolerably regular intervals, the f gecal 

 matter is passed into the rectum and is then almost immediately discharged 

 from the body. 



DefcBcation. In health, expulsion of faecal matters takes place with regu- 

 larity generally once in the twenty-four hours. This rule, however, is by no 

 means invariable, and dejections may habitually occur twice in the day or 

 every second or third day, within the limits of health. At the time when 

 defaecation ordinarily takes place, a peculiar sensation is experienced calling 

 for an evacuation of the bowels ; and if this be disregarded, the desire may 

 pass away, after a little time the act becoming impossible. It is probable 

 that the faeces are then passed out of the rectum by antiperistaltic action. 



The condition which immediately precedes the desire for defaecation is 

 probably the descent of the contents of the sigmoid flexure of the colon into 

 the rectum. It was formerly thought that the fasces constantly accumulated 

 in the dilated portion of the rectum, where they remained until an evacua- 

 tion took place ; but the arguments of O'Beirne against such a view are 

 conclusive. He demonstrated, by explorations in the human subject, that 

 under ordinary conditions, the rectum is contracted and contains neither 

 faeces nor gas. It is, indeed, a fact familiar to every surgeon, that the rec- 

 tum usually contains nothing which can be reached by the finger in physi- 

 cal examinations, and that paralysis or section of the muscles which close 

 the anus by no means involves, necessarily, a constant passage of faecal mat- 

 ter. O'Beirne not only found the rectum empty and presenting a certain 

 degree of resistance to the passage of injected fluids, but on passing a stom- 

 ach-tube into the bowel, after penetrating six to eight inches (15 to 20 cen- 

 timetres), it passed into a space in which its extremity could be moved with 

 great freedom, and there was instantly a rush of flatus, of fluid faeces, or of 

 both, through the tube. In some instances in which nothing escaped through 

 the tube, the instrument conveyed to the hand an impression of having en- 

 tered a solid mass ; and on being withdrawn it contained solid faeces in its 



