200 TEXT-BOOK OF PHYSIOLOGY 



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. 85). 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 

 a contraction of the circular fibers behind the mass of food and a relaxation 

 of the fibers in advance of it. The result is a movement forward of the food, 

 and as it moves it is followed by a ring of constriction and preceded by a 

 ring of relaxation or inhibition. The rate of movement of the peristaltic wave 

 is usually extremely slow except in the duodenal region where it is quite rapid. 



The first of these two movements to make its appearance is the peristaltic 

 which arises at the upper portion of the duodenum from which it sweeps 

 downward with considerable rapidity, carrying with it the food which has 

 been discharged from the stomach and which has accumulated in this region. 

 From the appearance, as shown by Rontgen ray examination, which the 



