MECHANICAL PHENOMENA. 



27 



3, in which two-thirds of an original segment is present on 

 the right-hand end of the string of food and one-third on 

 the left hand. Not until the third division occurs along the 

 dotted line c is the original arrangement of the segments 

 restored. 



The rapidity with which the segmenting movements occur 

 is exceedingly interesting. If each segmentation, that is to 

 say, if every change from one line to another in the diagrams ; 

 is counted, it is found that from twenty-eight to thirty occur 

 each minute. If the string of food is thin, only rarely does 

 the rate fall as low as twenty-three in the same unit of time. 

 When much food is present in a given segment of intestine, 



FIG. 6. 



(Copied from CANNON: American Journal of Physiology, 1902, 

 VI, p. 258.) 



as indicated in Fig. 6, the number may fall as low as eighteen 

 to twenty-one per -minute. 



CANNON has calculated that a slender string of food may 

 commonly undergo division into small segments more than 

 a thousand times without changing its position in the intes- 

 tine. The admirable purpose which this serves in thoroughly 

 mixing the food with the digestive juices and bringing it in 

 contact with the absorbing mucous lining of the intestine 

 will at once become apparent. Moreover, as MALL l has 

 pointed out these repeated rhythmical contractions greatly 



1 MALL: Johns Hopkins Hospital Reports, I, p. 37. 



