622 DIGESTION. 



moved about freely in a space, which, on introducing the finger, was 

 ascertained to be the pouch of the rectum ; but that from the highest 

 part of the pouch to the upper extremity of the gut generally a 

 distance of from six or seven to eight inches it could not be passed 

 upwards without meeting with considerable resistance, and without 

 using a degree of force to mechanically dilate the intestine, which was 

 plainly felt to be so contracted as to leave no cavity for this extent; 

 that when the instrument reached, in this way, the highest point of the 

 rectum, the resistance to its passage upward was felt to be sensibly 

 increased, until, at length, by using a proportionate degree of pressure, 

 it passed rapidly forward, as if through a ring, into a space in which 

 its extremity could be moved with great freedom, and as instantly a 

 rush of flatus, of fluid faeces, or of both, took place through the tube ; 

 and that in every instance, where the tube presented the least appear- 

 ance of faeces after being removed, this appearance was confined to that 

 portion which had entered the sigmoid flexure: guided by these and 

 other facts, Dr. O'Beirne properly concluded, that in the healthy and 

 natural state, all the part of the rectum above its pouch is at all times, 

 with the single exception of a few minutes previous to the evacuation 

 of the bowels, firmly contracted, and perfectly empty, at the same time 

 that the pouch itself, as well as the sigmoid flexure of the colon, is 

 always more or less open, and pervious, and that the sphincter ani 

 muscles are but subsidiary agents in retaining the faeces. When the 

 faeces are firm, considerable muscular effort is necessary to expel them; 

 but when they are of a softer consistence, the contraction of the rectum 

 is sufficient. 



The sphincters as elsewhere shown afford examples of reflex 

 action. After sensation and volition are suspended, they contract 

 under direct irritation. Yet, like the respiratory muscles, they are of 

 a mixed character, partly voluntary and partly involuntary. They 

 are involuntary, but capable of being aided or impeded by a voluntary 

 effort. The state of gentle contraction, in which they constantly are, 

 is evidently dependent upon their connexion with the spinal cord; for 

 the experiments of Dr. Marshall Hall have exhibited, that it ceases, 

 when the connexion is destroyed. 



Air, contained in the intestinal canal, readily moves about from place 

 to place, and speedily reaches the rectum by the peristaltic action 

 alone. Its expulsion, however, is commonly accomplished by the aid 

 of the abdominal muscles; when it issues with noise. If discharged by 

 the contraction of the rectum alone, it is generally in silence. Children 

 are extremely subject to flatulence; in the adult it is not so common. 

 Certain kinds of diet favour its production more than others, especially 

 in those of weak digestive powers, of which condition its undue evolu- 

 tion is generally an indication. The leguminous and succulent vegeta- 

 bles in general belong to this class. Where digestion is tardily accom- 

 plished, they give occasion to the copious disengagement of gas. Too 

 often, however, the disgusting habit of constantly discharging air stre- 

 perously from the bowels is encouraged, rather than repressed; and 

 there are persons, who are capable of effecting the act almost as fre- 

 quently as they attempt it. 



