obs 



MECHANICAL PHENOMENA. 25 



When sufficient time has elapsed so that the food has been 

 distributed through the intestine as indicated in Fig. 4, and 

 the animal is exposed to the -rays, it is found that most 

 of the loops are in a state of perfect rest. This is due only 

 to the excited state of the animal. After a time, if the 

 cat is allowed to remain quiet, the intestinal movements 

 begin. Two chief kinds of intestinal movement may then 

 be recognized: first, movements of rhythmic segmentation, 

 and secondly, peristaltic movements. By far the more com- 

 mon of these two movements is the first named. Sway- 

 ing movements, such as have been described by the older 

 ervers, are also seen at times. 



The character of the rhythmic segmentation can be best un- 

 derstood by reference to Fig. 5. The movements consist 

 essentially in the sudden division of one of the long narrow 

 strings of food lying in one of the loops shown in Fig. 4 

 into a large number of segments of nearly equal size, These 

 segments are ttien suddenly divided and neighboring halves 

 unite to form^iew segments, after which the process is re- 

 peated. This division and redivision of the food follow each 

 other many times in succession. In line 1 of Fig. 5 is shown 

 "the food as it lies in a loo^f intestine in the quiescent state. 

 Suddenly as the movemen^rof rhythmic segmentation evidence 

 themselves, this string of food is divided into a large number 

 of nearly equal segments as indicated in line 2. A moment 

 later each of these segments is divided injjwo pieces, and 

 the neighboring pieces unite to form a new^egment. Thus 

 a and 6 of line 2 unite to form the segment cJjji line 3. When 

 this division occurs the end segments A an^jp remain small. 

 But the next segmentation which divides the segments of 

 line 3 restores the old order of things, for the end pieces re- 

 unite with the halves of their adjoining segments to form 

 the new segments indicated in line 4. This series of seg- 

 ments it will be seen corresponds to the series shown in 

 line 2. The process of division and redivision of the food 

 continues under ordinary circumstances uninterruptedly for 



