458 DIGESTION 



the pyloric sphincter about the same time as normally, but the subse- 

 quent evacuation was very much accelerated, because no acid came in 

 contact with the duodenal mucosa. Water and egg white may leave 

 the stomach independently of any acid reflex control of the pylorus. By 

 observations made through a duodenal fistula it has been found that, 

 after a quantity of water has been swallowed, most if not all of it very 

 soon enters the duodenum in a more or less continuous stream. It is no 

 doubt on this account that drinking contaminated water is especially 

 dangerous on an empty stomach. 



The nervous pathway through which these acid reflexes take place has 

 been shown to be the myenteric plexus. Indeed, the whole mechanism 

 is quite analogous with that which Ave shall see occurs in the intestine 

 during peristalsis : the stimulus, that is, the acid, causes a contraction 

 of the gastric tube behind it and a dilatation in front. 



Fig. 158. — Outlines of shadows in abdomen obtained by exposure to x-rays 2 hours after 

 feeding with food containing bismuth subnitrate. The food in A was lean beef, and in B boiled 

 rice. The smaller size of the stomach shadow and the much greater total area of the intestinal 

 shadows in B than in A show that carbohydrate leaves the stomach earlier than protein. (From 

 Cannon.) 



Rate of Emptying - of Stomach 



The relationship of these facts to the rate at which different foodstuffs 

 leave the stomach is very readily explained. The method for investigat- 

 ing this problem, which again we owe to Cannon, consists in feeding ani- 

 mals with a strictly uniform amount of different foods made up, as 

 nearly as possible, of equal consistency and containing bismuth subni- 

 trate in the proportion of 5 gm. to each 25 c.c. By feeding such mix- 

 tures to cats previously starved for twenty-four hours, and examining 

 the abdomen by the x-ray at regular intervals, the shadows cast by the food 

 after passage into the intestine can be outlined on tracing paper, and 

 the total length* measured (Fig. 158). In taking this as an estimate of 

 the amount of food in the intestine, several errors are no doubt incurred 



'This is permissible since the shadows are practically all of the same width. 



