CHAP. XXV.] INTESTINAL DIGESTION. 237 



that substances introduced into the highest part of the intestinal 

 canal take a certain time, varying in each particular case, to traverse 

 it. For example, the act of defsecation will, if allowed or encouraged, 

 take place with the utmost regularity every twelve or twenty-four 

 hours, and the quantity discharged will exhibit but little variation, 

 the quantity and quality of the food remaining the same ; and indi- 

 gestible substances taken with the food, seeds, husks, skins, etc., 

 will at certain intervals appear in the faeces, having traversed the 

 whole canal. There is no act of the animal economy more strikingly 

 under the influence of habit, i.e., under the control of physical 

 causes, without mental interference, than this of defsecation ; nor, 

 on the other hand, is there any act which may be more completely 

 deranged by its being baulked, through the resistance which the 

 will can oppose to it. The intestinal movements are partly due to 

 the influence of the stimulus of distension upon the muscular tunic, 

 and partly to the reflex action of the ganglia of the intestinal por- 

 tion of the sympathetic, stimulated by the contact of the intestinal 

 contents with the mucous membrane. Direct irritation of the 

 solar plexus, or of the semilunar ganglia produces a marked in- 

 crease in the movements of the intestines. ( Vide p. 145, vol. ii.) 



When obstruction exists at a certain point of the bowels, they 

 become dilated above that point, and when the dilatation has at- 

 tained a certain amount, their contents are found to flow back into 

 the stomach, and are ejected by vomiting. This is commonly sup- 

 posed to be due to an inverted direction of the action of the 

 muscular tunic of the intestines (antiperistaltic action). But Dr. 

 Brinton has very ably shewn that there is no antiperistalsis of the 

 bowels under these circumstances, anymore than of the stomach in 

 vomiting, and that the altered course of the fluids is due simply to 

 their reflux along the axis of the intestine from the seat of obstruc- 

 tion. The muscular coat of the bowels acting in the downward 

 direction, and with force proportionate to the obstacle, propels the 

 fluids to a point where they encounter insuperable resistance, and 

 whence they must take the course which affords least or no obstacle. 

 Thus a backward current is established in that part of the fluid 

 least influenced by the walls of the intestine, that namely, which 

 occupies its axis, or, in Dr. Brinton's words, " an axial reversed 

 current is developed, which returns matters from the neighbourhood 

 of the strangulation to some higher point in the canal." When 

 fluid returns along the sides of a syringe with a piston not water- 

 tight, we have a somewhat analogous phenomenon, and we may 

 imitate the reversed movement of the intestinal fluids by trying to 



