DIGESTION 267 



ascending colon, forcing some of the food onwards ; a 

 moment later antiperistaltic waves begin, which drive 

 the food back again into the csecal pouch, thus churning 

 the contents up and exposing them to the absorbing 

 wall. It is here that the absorption of the remains of 

 the nutritive constituents of the food takes place, as well 

 as that of most of the water, for the contents of the 

 transverse colon are usually nearly as solid as those of 

 the sigmoid. 



As material accumulates in the transverse colon, deep 

 waves of constriction appear one after the other and 

 carry the material into the descending colon, leaving 

 the ascending and transverse portions free for the occur- 

 rence of antiperistalsis. 



The occurrence of antiperistalsis as a normal process 

 in the upper part of the colon makes clear the signifi- 

 cance of the ileo-caecal valve, which is competent for the 

 amount and character of the material normally dis- 

 charged from the ileum. It can be overcome, however, 

 by large injections of fluid from below, which has been 

 proved both experimentally* and by observations on 

 patients with a fistula of the ileum,t as well as by 

 accumulated instances of the vomiting of enemata.J 



Fig. 18 shows the average rate at which the colon is 

 traversed by a bismuth meal according to the observation 

 of Hertz. 



* Griitzner Pfluger's ArcJiiv, 1898, Ixxi. 492. 



j- See Neucki, etc., loc. cit. 



J See Mohroof, Indian Med. Gaz. 1902, xxxvii. 394. 



Loc. cit. 



