648 PHYSIOLOGY OF DIGESTION AND SECRETION. 



The small intestine and the greater part of the large intestine 

 receive visceromotor nerve fibers from the vagi and the sympathetic 

 chain. The former, according to most observers, when artifically 

 stimulated cause movements of the intestine, and are therefore 

 regarded as the motor fibers. It seems probable, however, that the 

 vagi carry or may carry in some animals inhibitory fibers as well, 

 and that the motor effects usually obtained upon stimulation are 

 due to the fact that in these nerves the motor fibers predominate. 

 The fibers received from the sympathetic chain, on the other hand, 

 give mainly an inhibitory effect when stimulated, although some 

 motor fibers apparently may take this path. Bechterew and 

 Mislawski * state that the sympathetic fibers for the small intestine 

 emerge from the spinal cord as medullated fibers in the sixth dorsal 

 to the first lumbar spinal nerves, (or lower Bunch) and pass to the 

 sympathetic chain in the splanchnic nerves and thence to the 

 semilunar plexus. 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. 



Movements of the Large Intestine. 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 



* " Archiv f . Physiologie, " 1889, suppl. volume. 



