1014 DIGESTION 



fibers must constrict its lumen, whereas the contraction of the longi- 

 tudinal fibers must render that particular segment more bulky and 

 enlarge its capacity. Ordinarily, however, these two movements are 

 combined into what is known as the peristaltic wave, which consists of 

 a zone of constriction and an anteceding zone of relaxation. These 

 peristaltic waves may proceed either from above downward or from 

 below upward. The former constitute the regular peristaltic waves 

 and the latter, the antiperistaltic waves. We shall see later that anti- 

 peristalsis is the chief movement of the beginning portion of the large 

 intestine, while regular peristalsis is the principal movement of the 

 small intestine. Antiperistalsis is observed here only under abnormal 

 conditions. A second type of movement executed usually by the small 

 intestine, is the so-called pendular motion. It consists of alternate 

 constrictions and relaxations of neighboring segments of the gut, which 

 are repeated with a definite regularity or rhythm. 





Fro. 515. DIAGRAM TO SHOW THE EFFECT OF THE RHYTHMICAL CONSTRICTING MOVE- 

 MENTS OF THE SMALL INTESTINE UPON THE CONTAINED FOOD. 



A string of food (1) is divided suddenly into a series of segments (2); each of the 

 latter is again divided and the process is repeated a number of times (3 and 4). Even- 

 tually a peristaltic wave sweeps these segments forward a certain distance and gathers 

 them again into a long string , as in (1). The process of segmentation is then repeated 

 as described above. (Cannon.) 



When the chyme is ejected into the duodenum, it is forced against 

 the upper surfaces of the valvulse conniventes which stretch across the 

 lumen of the subpyloric canal in the form of incomplete transverse 

 partitions. In consequence of this initial impediment to its rapid 

 onward flow, the chyme is collected in a single mass well above the 

 orifices of the biliary and pancreatic ducts. Now begins its subdivision 

 into smaller portions by the pendular or rhythmic movements. A 

 comprehensive study of these has been made by Griitzner 1 who was 

 able to analyze them by mixing insoluble substances, such as nitrate 

 of bismuth, with the ingesta. More recently, Cannon 2 has studied 

 them with the help of the Rontgen rays. Constrictions appear here 

 and there which split the formerly large mass into numerous smaller 

 ones. Moreover, these constrictions appear in a perfectly regular order 

 soTthat the original mass is divided first into two, then into four, then 

 into eight, and more. These smaller portions are then reunited into 



1 Pfluger's Archiv, Ixxi, 1898. 



2 Am. Jour, of Physiol., i, 1898, and vi, 1902. 



