MOVEMENTS OF THE ALIMENTARY CANAL. 735 



except in the cervical and upper part of the thoracic region, it 

 was found that the animal, after it had recovered from the 

 operation, had normal movement once or twice a day, indicating 

 that the rectum and lower bowels acted by virtue of their 

 intrinsic mechanism. An interesting result of these experi- 

 ments was the fact that the external sphincter suffered no 

 atrophy, although its motor nerve was destroyed, and that it 

 eventually regained its tonic activity. 



It would seem that the whole act of defecation is, at bottom, 

 an involuntary reflex. The physiological center for the move- 

 ment probably lies in the lumbar cord, and it has sensory and 

 motor connections with the rectum and the muscles of defecation. 

 As stated above, the inhibitory fibers to the internal sphincter 

 pass by way of the hypogastric nerve, the motor fibers through 

 the nervus erigens, and both of these nerves contain afferent 

 fibers which may reflexly excite inhibition or contraction. But 

 this center is probably provided also with intraspinal con- 

 nections with the centers of the cerebrum, through which the 

 act may be controlled by voluntary impulses and by various 

 psychical states; the effect of emotions upon defecation being 

 a matter of common knowledge. In infants the essentially in- 

 voluntary character of the act is well known. 



Vomiting. The act of vomiting causes an ejection of the con- 

 tents of the stomach through the esophagus and mouth to the 

 exterior. It was long debated whether the force producing this 

 ejection comes from a strong contraction of the walls of the stom- 

 ach itself or whether it is due mainly to the action of the walls of 

 the abdomen. A forcible spasmodic contraction of the abdominal 

 muscles takes place, as may easily be observed by any one upon 

 himself, and it is now believed that the contraction of these muscles 

 is the principal factor in vomiting. Magendie found that if the 

 stomach was extirpated and a bladder containing water was sub- 

 stituted in its place and connected with the esophagus, injection 

 of an emetic caused a typical vomiting movement with ejection of 

 the contents of the bladder. Gianuzzi showed, on the other hand, 

 that upon a curarized animal vomiting could not be produced by an 

 emetic because, apparently, the muscles of the abdomen were 

 paralyzed by the curare. There are on record a number of ob- 

 servations which tend to show that the stomach is not passive 

 during the act. On the contrary, it may exhibit contractions, more 

 or less violent in character. According to Openchowski,* the 

 pylorus is closed and the pyloric end of the stomach firmly con- 

 tracted so as to drive the contents toward the dilated cardiac por- 

 tion. Cannon states that in cats the normal peristaltic waves pass 

 * Openchowski, "Archiv f. Physiologie," 1889, p. 552. 



