726 PHYSIOLOGY OF DIGESTION AND SECRETION. 



to some observers stimulation of portions of the cerebral cortex 

 may produce movements or relaxation of the walls of the small and 

 large intestines. 



Effect of Various Conditions upon the Intestinal Move- 

 ments. — ^Experiments have shown that the movements of the in- 

 testines may be evoked in many ways in addition to direct stimu- 

 lation of the extrinsic nerves. Chemical stimuli may be applied 

 directly to the intestinal wall. Mechanical stimulation — pinching, 

 for example, or the introduction of a bolus into the intestinal 

 cavity — may start peristaltic movements. Violent movements 

 may be produced also by shutting off the blood-supply, and again 

 temporarily when the supply is re-established. A condition of 

 dyspnea may also start movements in the intestines or in some 

 cases inhibit movements which are already in progress, the stimu- 

 lus in this case seeming to act upon the central nervous system and 

 to stimulate both the motor and the inhibitory fibers. Oxygen gas 

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

 tine, while CO2, CH4, and HjS 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 thoracic autonomic 

 fibers received by way of the splanchnic nerve and superior mesen- 

 teric ganglion.* 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 infrequent, 

 so that the material received from the small intestine is slowly 

 moved along while becoming more and more sohd from the loss 

 of water. The contents of the ascending colon are soft and semi- 

 liquid, but in the distal end of the transverse colon they attain 

 the consistency of the feces. 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, corresponding roughly 

 to the descending and distal portion of the transverse colon, the 

 food is moved toward the rectum by peristaltic waves. 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 



* Elliott, "Journal of Physiology," 1904, 31, 157. 

 t Cannon, hoc. cit. 



