VOMITING. 59 



of saliva. The saliva, mixed with air, accumulates to a consider- 

 able extent at the lower end of the oesophagus and thus 

 distends it. A forced inspiration is now made, during the 

 first stage of which the glottis is open so that the air enters 

 the lungs, but later the glottis closes so that the in- 

 spired air is sucked into the oesophagus, which, already 

 somewhat distended by saliva, now becomes markedly so. The 

 abdominal muscles then contract so as to compress the stomach 

 against the diaphragm and, simultaneously, the cardiac sphincter 

 relaxes, the head is held forward and the contents of the stomach 

 are ejected through the previously distended oesophagus. The 

 compression of the stomach by the contracting abdominal mus- 

 cles is assisted by an actual contraction of the stomach itself, 

 as has been clearly demonstrated by the X-ray method. (See p. 

 58.) After the contents of the stomach itself have been evac- 

 uated, the pyloric sphincter may also relax and thus permit the 

 contents (bile, etc.) of the duodenum to be vomited. 



The act of vomiting is controlled by a center located in the 

 medulla, and the afferent fibers to this center may come from 

 many different regions of the body. Perhaps the most potent 

 of them come from the sensory nerve endings of the fauces and 

 pharynx. This explains the tendency to vomit when the mucosa 

 of this region is mechanically stimulated. Other afferent im- 

 pulses come from the mucosa of the stomach itself, and these are 

 stimulated by swallowing certain drugs called emetics, import- 

 ant among which are strong salt solution, mustard water, zinc 

 sulphate, etc. When some poisonous substance has been swal- 

 lowed, the immediate treatment is to give one of these emetics 

 and thus cause the poison to be vomited. Certain other emetics, 

 particularly tartar emetic and apomorphine, act on the vomiting 

 center itself, and can therefore act when given subcutaneously. 

 Afferent vomiting impulses also arise from the abdominal vis- 

 cera, thus explaining the vomiting which occurs in strangulated 

 hernia, and in other irritative lesions involving this region. 



