FOOD AND DIGESTION. 369 



concerned, has been disproved by experiments of Pavy's, in which the 

 mucous membrane of the stomachs of dogs was dissected off for a small 

 space, and, on killing the animals some days afterward, no sign of diges- 

 tion of the stomach was visible. " Upon one occasion, after removing 

 the mucous membrane, and exposing the muscular fibres over a space 

 of about an inch and a half in diameter, the animal was allowed to live 

 for ten days. It ate food every day, and seemed scarcely affected by 

 the operation. Life was destroyed while digestion was being carried on, 

 and the lesion in the stomach was found very nearly repaired; new mat- 

 ter had been deposited in the place of what had been removed, and the 

 denuded spot had contracted to much less than its original dimensions." 

 Pavy believes that the natural alkalinity of the blood, which circu- 

 lates so freely during life in the walls of the stomach, is sufficient to 

 neutralize the acidity of the gastric juice; and as may be gathered from 

 what has been previously said, the neutralization of the acidity of the 

 gastric secretion is quite sufficient to destroy its digestive powers; but 

 the experiments adduced in favor of this theory are open to many objec- 

 tions, and afford only a negative support to the conclusions they are in- 

 tended to prove. Again, the pancreatic secretion acts best on proteids 

 in an alkaline medium; but it has no digestive action on the living in- 

 testine. No satisfactory theory of the reason why the stomach does not 

 digest itself has yet been suggested. , 



VOMITING. 



The expulsion of the contents of the stomach in vomiting, like that 

 of mucus or other matter from the lungs in coughing, is preceded by 

 an inspiration; tjie glottis is then closed, and immediately afterward the 

 abdominal muscles strongly act; but here occurs the difference in the 

 two actions. Instead of the vocal cords yielding to the action of the ab- 

 dominal muscles, they remain tightly closed. Thus the diaphragm being 

 unable to go up, forms an unyielding surface against which the stomach 

 can be pressed. In this way, as well as by its own contraction, the dia^ 

 phragm is fixed, to use a technical phrase. At the same time the cardiac 

 sphincter-muscle being relaxed, and the orifice which it naturally guards 

 being actively dilated, while ihz pylorus is closed, and the stomach itself 

 also contracting, the action of the abdominal muscles, by these means 

 assisted, expels the contents of the organ through the oesophagus, 

 pharynx, and mouth. The reversed peristaltic action of the oesophagus 

 probably increases the effect. 



It has been frequently stated that the stomach itself is quite passive 

 during vomiting, and that the expulsion of its contents is effected solely 

 by the pressure exerted upon it when the capacity of the abdomen is di- 

 minished by the contraction of the diaphragm, and subsequently of the 

 abdominal muscles. The experiments and observations, however, which 

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