THE MECHANISMS OF DIGESTION 



453 



stomach has become filled, peristaltic waves are seen to take their 

 origin about the middle of the body of the stomach, and to course 

 towards the pylorus. Above the region at which these waves originate 

 that is, the cardiac half of the body of the stomach and all of the 

 fundus there are no waves, but as digestion proceeds the w^alls slowly 

 and steadily contract on the mass of food. This so-called cardiac pouch 

 does not, however, dimmish in size so rapidly as the part of the body of 

 the stomach over which the peristaltic waves are passing. The circular 

 fibers of the walls of this part of the stomach sometimes called the 

 gastric tube contract tonically, so that it becomes tubular in form, 

 with the full cardiac pouch at the left and above and the pyloric por- 



Fig. 156. Outlines of the shadows cast by the stomach at intervals of an hour each after feeding 

 a cat with food impregnated with bismuth subnitrate. (From Cannon.) 



tion at the right. The latter portion meanwhile does not diminish much 

 in size, although the peristaltic waves traveling over it are very pro- 

 nounced. As will be clear from the figure, these changes in outline go 

 on until the cardiac pouch has become practically empty and the food 

 has been all moved along the now tubular portion of the body into the 

 pyloric vestibule. 



From this description it is evident that the function of the cardiac 

 end is to serve as a reservoir for the food, which, by a slow contraction 

 of the walls, is gradually delivered into the gastric tube, where, by 

 peristalsis it is carried towards the pyloric vestibule. 



The time required for the peristaltic waves to travel from their place 

 of origin to the pylorus is considerably longer than the interval between 



