104 THE PHYSIOLOGY OF VOMITING 



ruminating actions, and are presided over by a nerve-centre 

 in the medulla. The ganglia regulating respiration and 

 vomition lie close together. Certain cells probably take 

 part in both actions, and are acted upon by the same agents. 

 ' Emetics usually quicken the respiration considerably before 

 they produce vomiting, and, if injected into the veins, they 

 not only quicken the respiration, but prevent the condition 

 of apnoea being produced by vigorous artificial respiration. 

 On the other hand, the desire to vomit may be lessened, to 

 some extent, by taking frequent and deep inspirations, and 

 narcotics which diminish the excitability of the respiratory 

 centre also lessen the tendency to vomit.' 



That the vomiting centre, rather than the stomach itself, 

 is the prime factor in the production of emesis, is evident 

 fromMagendie's famous experiment of removing the stomach 

 of a dog, attaching to the severed oesophagus a pig's bladder 

 filled with fluid, which, when tartar emetic was injected into 

 the veins, was compressed between the abdominal muscles 

 and the diaphragm, and emptied of its contents by vomiting. 



When the fauces of men, dogs, or other animals which 

 vomit readily, are tickled with a feather, or when the interior 

 of the stomach is irritated mechanically, or by a solution of 

 mustard, the stimulus is conveyed by afferent nerves to the 

 vomiting centre with which the special motor impulses are 

 correlated. Many other parts of the body, through their 

 afferent nerves, have communication with the vomiting 

 centre, and hence vomiting is produced, not only by irrita- 

 tion of the fauces and stomach, but by irritation of the brain, 

 lungs, liver, and gall ducts, the intestines, kidneys, and 

 bladder, sometimes even by pain or injury of the extremities. 



Dogs, cats, and pigs vomit as readily as men. Indeed, in 

 dogs, vomiting is induced by most disagreeably-tasted, 

 nauseous, or acrid substances, and sometimes is brought on 

 purposely by the eating of grass. But horses, ruminants, 

 rabbits, and guinea-pigs rarely if ever vomit, and are in- 

 sensible to the action of powerful emetics. In horses emesis 

 only occurs from extreme distension and spasm of the 

 stomach, from dilatation of the lower part of the gullet, 

 from complete obstruction of the intestines, and from the 

 action of large doses of aconite, which, however, induce 



