MECHANICAL PHENOMENA. 53 



In order to ascertain the fate of enemas, CANNON intro- 

 duced various amounts of thick and thin food mixtures, 

 holding bismuth subnitrate powder in suspension, into the 

 previously cleaned rectum of various animals and observed 

 what happened by means of the z-rays. The enemas had 

 the following composition: 



100 c.c. milk, 

 2 grams starch, 

 1 egg, 

 15 grams bismuth subnitrate. 



To make the enemas thick all these were stirred together 

 and boiled to a soft mush. To have them thin the egg 

 was omitted until after boiling, when it was added to the 

 cooled mass. The amounts injected varied from 25 c.c. 

 to 90 c.c., which was about sufficient to fill the large bowel 

 of the animals experimented upon. 



Besides depending upon mere observation, radiographs 

 were taken at various intervals, in order to show the dis- 

 tribution of the injected enemas. After a control radio- 

 graph had shown the absence of any bismuth-containing 

 food in the intestine of the animal to be experimented upon, 

 the food was introduced into the rectum. It was found 

 in these experiments that when only small amounts are 

 injected they lie at first in the descending colon. In every 

 case, however, anti-peristaltic waves commence and the 

 food is carried through the transverse and ascending colon 

 into the caecum. Small injections of nutrient material 

 never pass this point. The larger injections, however, do 

 not stop when they reach the ileocaecal valve, but pass through 

 it high up into the small intestine. Strange as it may seem, 

 this valve, which is competent to the food passing through 

 it in the normal progress of the food from the stomach to 

 the rectum, allows the nutrient material from large rectal 

 enemas to pass through into the small intestine. The anti- 

 peristaltic waves of the ascending colon seem to be the 

 effective agents in forcing the enema backward through 



