200 TEXT-BOOK OF PHYSIOLOGY 



did not become ravenous until a few days before death. The animal usually 

 ate about a pound and a half of beef-heart daily, but always refused fat. 

 There was an absence at all times of jaundice, fetor of the breath, and fall- 

 ing of the hair. Post-mortem examination showed that the bile-duct was 

 obliterated, and there was no evidence that any bile could have passed into 

 the intestine. The results of this and similar cases go to show that that por- 

 tion of the bile which is secretory in character is essential to digestion and 

 the nutrition of the body that, though large quantities of food are con- 

 sumed, progressive diminution of weight takes place until nearly 40 per 

 cent, of the body is consumed. In some instances the breath becomes 

 fetid and there is a falling of the hair, showing some profound disturbance 

 of the general nutritive process. 



The Movements of the Small Intestine. During the period of intes- 

 tinal digestion, the walls of the intestine exhibit a series of movements which 

 triturate the food, mix it with the intestinal secretions, gradually transfer it 

 from the upper to the lower portions and promote the absorption of the pre- 

 pared food materials. The movements of the small intestine have been 

 studied by means of the Rontgen rays by Cannon. The method adopted 

 was to mix with the food subnitrate of bismuth, which being opaque rendered 

 the movements of the intestinal contents and thereby the movements of the 

 intestinal walls visible on the fluorescent screen. There investigations re- 

 vealed the presence of two forms of activity, one of which is more or less 

 stationary and due to rhythmic contraction of circular muscle-fibers, the other 

 progressive, passing from above downward and due to the contraction of 

 circular and longitudinal muscle-fibers. The former activity, which is by 

 far the more common, results in a division of the intestinal contents into 

 small segments and for this reason was termed by Cannon rhythmic seg- 

 mentation; the latter activity is the well-known peristaltic wave. 



Rhythmic Segmentation. When the abdominal cavity is investigated by 

 the method above mentioned, it is observed that after the food has passed 

 into the intestine and formed a more or less consistent mass of variable 

 length, bands of circular muscle-fibers, situated at regular distances one 

 from another, begin to contract and divide a mass of food into segments, 

 after which they at once relax to be followed by contraction of other bands in 

 the segments of the intestines overlying the segments of food. The result is 

 again a division of the food into two new segments (Fig. 83). The lower 

 half of each segment then unites with the upper half of the segment of food 

 below to commingle with it and expose new surfaces of the food mass to 

 contact with the actively absorbing mucosa. The continual repetition of 

 this process results in a thorough mixing of the food with the digestive juices. 

 From the manner in which these contractions make their appearance it would 

 seem that the mere presence of a segment of food in the lumen of the intestine 

 is sufficient to excite the overlying fibers to activity. 



In certain regions of the intestine rhythmic segmentation may continue 

 for half to three-quarters of an hour without moving the food forward to any 

 marked extent. In the cat the segmentation may proceed at the rate of 

 thirty divisions a minute. 



Peristalsis. After the food has been prepared by the process described 

 in the foregoing paragraph, it is then slowly carried downward by what is 

 known as the vermicular or peristaltic wave. This wave is characterized by 



