MOVEMENTS OF THE INTESTINE 



287 



also by swallowing, by brief inhalations of ether, by psychic influences, applica- 

 tion of cold to the abdomen and by direct stimulation (cf. infra). 



Attempts have been made by investigation of intestinal fistulas to deter- 

 mine the rate of propagation of the intestinal contractions, and different rates 

 have been observed which really was to be expected a priori, if one but con- 

 siders how much the degree of fullness and the nature of the contents must 

 affect the results. This consideration is confirmed by the observation made upon 

 an exsected intestine, that a contraction locally -produced is propagated along 

 the intestine only when it is induced by the moving contents. 



By observations on Vella fistula a value of 1 cm. in two to ten minutes, and 

 1 cm. in thirty to forty seconds, have been found for the rate of propagation of 

 intestinal contractions, the latter value after ingestion of food. According to 

 other observations the peristaltic wave would travel the entire length of the 

 intestine of a dog in about ninety minutes. Again, the velocity of the intestinal 

 movement has been estimated by passing a little 

 balloon fastened to a string through a stomach 

 fistula into the duodenum and measuring on the 

 string the rate at which the balloon was forced 

 along. In the uppermost parts the rate was 

 greater than in the lower parts, and in the former 

 reached the high value of 10-18 cm. in a minute. 

 In view of the long time the food sojourns in the 

 intestine this appears abnormally high. 



The intestine is of course constricted by the 

 contraction of its circular muscles; it is short- 

 ened and at the same time dilated by contraction 

 of its longitudinal muscles. Suppose, e. g., that 

 in Fig. 115 the small circles lying side by side 

 represent cross sections of the longitudinal mus- 

 cle fibers. When they contract, they become 

 thicker; each fiber therefore claims more space, 

 and the fibers lying side by side becoming thicker 

 all at once must have the effect of making the circumference larger i. e., of 

 dilating the lumen. This conclusion has been confirmed also experimentally 

 (Exner). 



FIG. 115. Schema to illustrate 

 the relation of the longitudinal 

 muscular fibers of the intestine 

 to each other. 



With regard to the movements actually taking place in the intestine within 

 the body, Cannon observed with the help of the Bontgen rays, after feeding a 

 food mixed with bismuth subnitrate, that the food in an intestinal loop is 

 divided all at once into small segments. From these segments new ones are 

 continually being formed by rhythmical contractions [what Cannon calls 

 u rhythmical segmentation"], at the rate of about thirty per minute. By 

 this means the food is very intimately mixed with the intestinal fluids and 

 is brought into close contact with the intestinal wall. The contents are then 

 pushed along and the process is repeated over and over (Fig. 116). 



The intestinal movements are to a certain extent independent of the 

 central nervous system, for an exsected intestine may contract spontaneously. 

 In animals whose nerves to the intestine have all been cut, two kind of 

 contractions may be observed. 



(1) The intestinal loops execute pendulum movements i.e., movements 

 to and fro, in which the longitudinal, and, to a less extent, the circular 



