DIGESTIOX 313 



over the antrum pylori. Ten or twelve similar waves follow, at 

 the end of which time the constriction in the region of the trans- 

 verse band divides the stomach into the firmly-contracted 

 antrum and the relaxed fundus. Now follows a sudden contrac- 

 tion 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 diffi- 

 culty. 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 be 

 excited by many afferent channels : the sensory nerves of the 

 fauces or pharynx, of the stomach or intestines (as in strangulated 

 hernia), of the liver or kidney (as in cases of gall-stone 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 Gowers). 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 

 efficient" afferent impulses may be set up, the gastric mucous 

 membrane, for example ; sulphate of zinc and sulphate of copper 

 act mainly in this way. Apomorphine, on the other hand, stimu- 

 lates the centre directly, and this is also the mode in which vomit- 

 ing is produced in certain diseases of the medulla oblongata. 

 The efferent nerves for the diaphragm are the phrenics, for the 

 abdominal muscles the intercostals. The impulses which cause 

 contraction of the stomach pass along the vagi. Dilatation of 

 the cardiac orifice is brought about by the inhibitory fibres in 

 the vagus already mentioned. 



