200 



DIGESTION 



The swinging motions of the intestine depend on the manner in which 

 loops of the gut are fastened posteriorly by the omentum. They are 

 produced by contraction of both the circular and the longitudinal mus- 

 cular fibers acting together, and occur every five or six seconds. They 

 are not influenced by nerves, but they are by temperature (Ludwig). 



'RHYTHMIC SEGMENTATION." 



O^^rVO 



Diagram of the intestinal movements: the solid lines show one phase of the movement, 

 and the dotted lines the other phase. 



By the aid of this complex movement (a combination of peristalsis, 

 shortening, and swinging), the first portion of an ordinary meal reaches 

 the cecum in about three hours, on an average, and it is at least six 

 hours more before the last part of such a meal passes through the 

 ileocecal valve. Thus, a bit of food requires three hours to pass the 



