736 PHYSIOLOGY OF DIGESTION AND SECRETION. 



the villi from the muscularis mucosse. If we can suppose that 

 they occur during normal digestion, it is evident that they add a 

 mechanical factor, not hitherto considered, which must help ma- 

 terially in the absorption of the products of digestion. 



The Nervous Control of the Intestinal Movements. There 

 is some evidence to show that the rhythmical contractions of the 

 intestines are muscular in origin (myogenic), while the more co- 

 ordinated peristaltic movements depend upon the intrinsic nervous 

 mechanism. The intestine is, however, not dependent for either 

 movement upon its connections with the central nervous system. 

 Like the stomach, it is an automatic organ whose activity is simply 

 regulated through its extrinsic nerves. 



The small intestine obtains its supply of extrinsic nerve-fibers 

 from two sources, a bulbar autonomic supply by way of the vagi 

 and a thoracic autonomic supply by way of the splanchnic nerves 

 and the superior mesenteric ganglia. Stimulation of the vagi causes 

 contraction or increased tonus in the intestinal musculature, while 

 stimulation of the splanchnics, on the contrary, causes relaxation or 

 inhibition of tonus.* The paths of these fibers through the central 

 nervous system are not known, but there are evidently connections 

 extending to the higher brain centers, since psychical states are 

 known to influence the movements of the intestine, and according 

 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 

 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. 



* For a discussion of the innervation of the small and large intestine, see 

 Gaskell, "The Involuntary Nervous System/' 1916. 



