430 THE HUMAN BODY 



to bring every particle of the contained food into intimate contact 

 with the intestinal walls, insuring thorough mixing with the in- 

 testinal secretions, and also favoring absorption. The liquid, 

 usually milky-looking, food mass in the small intestine is called 

 chyle. 



The onward movement of the food is secured by peristaltic 

 woves which start at the pylorus and run rather slowly along the 

 intestine. They are normally gentle movements, which do not 

 carry the chyle bodily before them, but move it forward little by 

 little. 



The mechanism of these intestinal movements is not entirely 

 clear, although it is believed that the peristaltic waves, and pos- 

 sibly also the segmentations, are special manifestations of the 

 myenteric reflex described above. 



Extrinsic Control of Stomach and Intestinal Movements. It 

 has been shown that normal movements of both stomach and in- 

 testine may go on in animals in which the nerves leading to these 

 organs from the central nervous system are cut. To a certain ex- 

 tent, therefore, they, like the heart, contain within themselves the 

 essential requirements for normal activity. Like the heart, how- 

 ever, they are subject to reflex control through the central nervous 

 system. 



The vagus nerves carry sympathetic fibers which when stimu- 

 lated arouse the stomach and intestine to activity. Stimulation 

 of the splanchnics inhibits their activity; hence these nerves must 

 contain inhibitory fibers. Both these sets of nerves are under 

 reflex control. Violent emotions, as of anger or anxiety, may bring 

 about reflex inhibition of the stomach and intestinal movements, 

 with serious impairment of the digestive process. 



Movements of the Large Intestine. During the passage of the 

 chyle through the small intestine the greater part of its nutritive 

 content is absorbed, but practically none of the water, so that it 

 is delivered through the ileocolic valve to the large intestine in a 

 very watery condition. The parts of the large intestine next to 

 the small intestine, the ascending and transverse colon, show an 

 interesting movement in the form of an antiperistalsis. This is a 

 peristaltic wave which begins in the transverse colon and sweeps 

 toward the ileocolic valve. It would tend to force the material 

 within the colon back into the small intestine did not the ileocolic 



