DISEASES OF THE DIGESTIVE ORGANS 35 



the contents of the stomach are forced upward and forward. 

 Vomiting is under the control of the centre of vomition (a paired 

 centre situated in the region of the calamus scriptorius). This 

 centre can be directly stimulated through the blood and indirectly 

 by stimulation of peripheral parts of the body, especially the 

 stomach. Emetics which can cause vomiting by acting through 

 the blood and stimulating the vomiting centre without necessarily 

 coming in contact with the stomach are called central or general 

 emetics. Apomorphine is a good example of this variety. Those 

 that cause vomiting reflexly by irritating the gastric mucous mem- 

 brane are called local or topical emetics. Examples are copper 

 sulphate, zinc sulphate, tartar emetic. Some emetics operate both 

 ways, e.g., emetin. Pathology teaches that vomiting may also be 

 caused reflexly by the irritation of numerous peripheral parts out- 

 side of the stomach, as the mucous membrane of the base of the 

 tongue, the throat, oesophagus, intestines, uterus, pelvis of the 

 kidney and gall ducts, and the terminations of the auricular branch 

 of the vagus (otorrhoea). Centric vomiting may also occur in dif- 

 ferent diseases of the brain and in uraemia. Finally, stimuli applied 

 to centres related to the centre of vomition appear to pass readily 

 over the latter. Hydrocyanic acid, which stimulates the respira- 

 tory centre, may exert a similar action upon the centre of vomition. 

 The drugs that have a specific stimulant effect upon the vagus 

 centre (digitalis, squill, strophanthus) may also stimulate the 

 vomiting centre. 



The effects of vomiting upon the stomach and other organs of 

 the body are very extensive. In the first place, the stomach, 

 oesophagus, pharynx and to a certain extent the buccal cavity are 

 emptied. The peristaltic movement of the stomach wall is 

 increased through the contraction of the gastric musculature. 

 Intestinal peristalsis is also increased, being stimulated reflexly by 

 the contraction of the stomach. Emetics which exert an espe- 

 cially pronounced action upon the intestines are called emeto- 

 cathartics. A further effect of vomiting is the reflex stimulation 

 of the secretion of the stomach and intestinal juices and of the 

 bile. The contraction of the inferior abdominal muscles exerts 



