DIGESTION 293 



cardiac orifice of the stomach, but may be a mere by-play 

 of the reflex stimulation bringing about the act. Tho 

 diaphragm is now forced down upon the abdominal 

 contents, the glottis closed, and the abdominal muscles 

 strongly contracted. At the same time the stomach itself, 

 and particularly the antrum pylori, contracts, the cardiac 

 orifice relaxes, and the gastric contents are shot up into 

 the pharynx, and issue by the mouth or nose. 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 For an animal whose stomach has been replaced by a bladder 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 administra- 

 tion 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. But in the adult such a contraction is, 

 ineffectual, and the same is the case in animals, for a dog under 

 the influence of a moderate dose of curara, which paralyzes 

 the voluntary muscles but not the stomach, cannot vomit. 



The nerve centre is in the medulla oblongata. It may bq 

 excited by many afferent channels : the sensory nerves of the; 

 fauces or pharynx, of the stomach or intestines (as ir* 

 strangulated hernia), of the liver or kidney (as in cases of 

 gallstone or renal calculi), of the uterus or ovary, and of the 

 brain (as in cerebral tumour), are all capable, when irritated, 

 of causing vomiting by impulses passing along them to the 

 vomiting centre. 



The vagus nerve in man certainly contains afferent fibres 

 by the stimulation of which this centre can be excited, 

 for it has been noticed that when the vagus was exposed 

 in the neck in the course of an operation, the patient 

 vomited whenever the nerve was touched (Boinet, quoted 

 by Cowers). In meningitis, vomiting is often a prominent 

 symptom, and is sometimes due to irritation of the vagus 

 nerve by the inflammatory process. 



Some drugs act as emetics by irritating surfaces in which 



