1018 DIGESTION 



impedes the progress of the contents of the ileum sufficiently, so that 

 the latter can advance into the cecum only in larger masses and under 

 a slight increase in pressure effected by the periodic peristaltic move- 

 ments of the ileum. 



The large intestine may be divided into four parts, namely, the 

 cecum with its vermiform appendix, and the ascending (proximal), 

 transverse (intermediate), and descending (distal) portions of the 

 colon. The movements observed here are very similar to those pre- 

 viously noted in the upper gut, i.e., they consist of peristaltic and pen- 

 dular motions. It is to be emphasized, however, that the latter are 

 now of little importance, whereas the antiperistaltic movements are 

 even more prominent than the peristaltic.^ It is also obvious that 

 the large intestine is much more quiescent than the small intestine, a 



Fig. 517. — Shadows of the Human Large Intestine Obtained by Means of the 



RONTGEN Rays. 

 I, Entrance of the contents of the ileum into the cecum and colon. II, the material 

 has progressed through the transverse colon as far as the splenic flexure, some has 

 escaped into rectum. Ill, the large intestine outlined by means of a solution of sub- 

 nitrate of bismuth injected through the rectum. 



fact which is in perfect agreement with the time required by the food 

 to traverse this channel. To illustrate, while the human stomach and 

 small intestine which measure about 7 m. in length, retain the food for 

 only about 7 to 9 hours, the large intestine which is only 1.5 m. in 

 length, cannot be passed in a much briefer time than 20 hours. Con- 

 sequently, the passage of the food from the mouth to the anus occu- 

 pies in all from 25 to 30 hours. An active alimentary canal, therefore, 

 would evacuate its contents once in about every 24 hours. 



On entering the ascending colon, the chyme incites antiperistaltic 

 waves which force it into the cecum. A regular peristaltic wave 

 then moves it upward toward the hepatic flexure, whence it is again 

 thrown back into the cecum by the antiperistalsis. These back and 

 forth movements continue for some time until the contents have lost 

 most of their water and gradually escape in a semisolid state into the 

 transverse colon. It is to be noted especially that these antiperistaltic 

 motions do not oppose the regular waves, but alternate with them and 

 1 Jacobi, Archiv fiir exp. Path, und Pharm., xxvii, 1890. 



