MOVEMENTS OF THE ALIMENTARY CANAL, 731 



within the bowels tends to suspend the movements of the intes- 

 tine, while CO 2 , CH 4 , and H 2 S act as stimuli, increasing the move- 

 ments. Organic acids, such as acetic, propionic, formic, and 

 caprylic, which may be formed normally within the intestine as 

 the result of bacterial action, act also as strong stimulants. 



Movements of the Large Intestine. The opening from the 

 small intestine into the large is controlled both by the ileocecal 

 valve and by a sphincter, the ileocecal or ileocolic sphincter. 

 It is stated that this sphincter is normally in tonus and that 

 its condition of tonus is regulated through the splanchnic nerve 

 (Magnus). The musculature in the large intestine has the 

 same general arrangement as in the small, and the usual view 

 has been that the movements are similar, although more infre- 

 quent, so that the material received from the small intestine 

 is slowly moved along while becoming more and more solid 

 from the absorption of water. The contents of the ascending 

 colon are soft and semiliquid, but in the distal end of the transverse 

 colon they attain the consistency of the feces. Bayliss and Starling 

 state that their law of intestinal peristalsis holds in this portion of 

 the intestine, that is, local excitation causes a constriction above 

 and a dilatation below the point stimulated. Cannon,* from his 

 studies of the normal movements in cats, as seen by the Roentgen 

 rays, comes to the conclusion that the movements in the proximal 

 portion of the large intestine show a marked peculiarity. He 

 divides the large intestine into two parts; in the second, correspond- 

 ing roughly to the descending and distal portion of the transverse 

 colon, the food is moved toward the rectum by peristaltic waves. 

 A number of constrictions may be seen simultaneously within a 

 length of some inches. In the ascending colon and cecum, on the 

 contrary, the most frequent movement is that of antiperistalsis. 

 The food in this portion of the canal is more or less liquid and its 

 presence sets up running waves of constriction, which pass toward 

 the ileocecal valve. These waves occur in groups separated by 

 periods of rest. They seem to originate from a constricted ring 

 which pulsates, each contraction starting an anastaltic wave. 

 The presence of the ileocecal valve prevents the material from 

 being forced back into the small intestine. The value of this 

 peculiar reversal of the normal movement of the bowels at this 

 particular point would seem to lie in the fact that it delays the 

 passage of the material toward the rectum, and by thoroughly 

 mixing it gives increased opportunities for the completion of the 

 processes of digestion and absorption. In animals with a saccu- 

 lated colon the separate sacs or haustra may exhibit rhythmic 



* Cannon, loc. cit. 



