498 



DIGESTION 



which will be made clear by consulting Fig. 161. This rhythmic seg- 

 mentation, as Cannon has called it, continues without cessation for more 

 than half an hour, and the food shadow does not meanwhile seem to change 

 its position in the abdomen to any extent. The splitting up of the seg- 

 ment and the rushing together of the neighboring halves proceed as a 

 rule with great rapidity; thus, if we count the number of different seg- 



Fig. 160. Apparatus for recording contractions of the intestine. (From Jackson.) 



ments during a definite period, we may find the rate of division in the 

 cat to be as high as 28 or 30 a minute. In man the divisions occur at a 

 frequency of approximately 10 per minute, which corresponds to the fre- 

 quency with which sounds can be heard when the abdomen is auscultated. 

 Although half an hour is the period which this process usually oc- 

 cupies, it may last considerably longer. In certain animals, such as the 

 rabbit, segmenting movements have not been observed, but instead 



