THE MECHANICAL PHENOMENA OF DIGESTION 329 



cardiac and pyloric sphincters of the stomach and the ileo-colic 

 sphincter and valve. But in certain circumstances the peristalsis 

 may be reversed, one or more of the guarded orifices forced, and the 

 onward stream of the intestinal contents turned back. In obstruc- 

 tion of the bowel, the faecal contents of the large intestine may pass 

 up beyond the ileo-caecal valve, and, reaching the stomach, be driven 

 by an act of vomiting through the cardiac orifice; in what is called*, 

 a ' bilious attack/ the contents of the duodenum may pass back 

 through the pylorus and be ejected in a similar way; or, what is 

 by far the most common case, the contents of the stomach alone 

 may be expelled. 



Vomiting is usually preceded by a feeling of nausea and a rapid 

 secretion of saliva, which perhaps serves, by means of the air 

 carried down with it when swallowed, to dilate the cardiac orifice 

 of the stomach, but may be a mere by-play of the reflex stimula- 

 tion bringing about the act. The diaphragm is now forced down 

 upon the abdominal viscera, first with open and then with closed 

 glottis. The thoracic portion of the oesophagus is thus placed 

 under diminished pressure, and therefore widened, while saliva and 

 air are aspirated into it out of the mouth. The abdominal muscles 

 strongly contract. At the same time the stomach itself, and par- 

 ticularly the antrum pylori, contracts, the cardiac orifice relaxes, 

 and the gastric contents are shot up into the lax oesophagus, and 

 through it into the pharynx, and issue by the mouth or nose. The 

 movements of the stomach during vomiting induced by apomorphine 

 have been studied in the cat by the Rontgen ray method. There is 

 first observed extreme relaxation of the cardiac end; then a deep 

 constriction appears a little below the cardiac orifice, and runs 

 towards the pylorus, increasing in depth as it goes. When the 

 transverse band is reached, this contracts firmly and remains con- 

 tracted, and the constriction passes on over the antrum pylori. 

 Ten or twelve similar waves follow, at the end of which time the 

 constriction in the region of the transverse band divides the stomach 

 into the firmly-contracted antrum and the relaxed fundus. Now 

 follows a sudden contraction of the diaphragm and abdominal 

 muscles accompanied by the opening of the cardiac orifice. Either 

 the diaphragm and abdominal muscles alone, without the stomach, 

 or the diaphragm and stomach together, without the abdominal 

 muscles, can carry out the act of vomiting. For an animal whose 

 stomach has been replaced by a bladder filled with water can be 

 made to vomit by the administration of an emetic (Magendie); 

 and Hilton saw that a man who lived fourteen years after an injury 

 to the spinal cord at the height of the sixth cervical nerve, which 

 caused complete paralysis below that level, could vomit, though 

 with great difficulty. In a young child in which very slight causes 

 will induce vomiting, the stomach alone contracts during the act. 



