DIGESTION. 257 



the process of digestion, being occasionally followed by death from ina- 

 nition; yet the digestive powers of the stomach may be completely 

 restored after the operation, and the formation of chyme and the nutri- 

 tion of the animal may be carried on almost as perfectly as in health. 

 This would indicate the existence of a special local nervous mechanism 

 which controls the secretion. 



Bernard found that galvanic stimulus of these nerves excited an 

 active secretion of the fluid, while a like stimulus applied to the sympa- 

 thetic nerves issuing from the semilunar ganglia, caused a diminution 

 and even complete arrest of the secretion. 



The influence of the higher nerve-centres on gastric digestion, as in 

 the case of mental emotion, is too well known to need more than a 

 reference. 



Digestion of the Stomach after Death. If an animal die during 

 the process of gastric digestion, and when, therefore, a quantity of gastric 

 juice is present in the interior of the stomach, the walls of thisorgan 

 itself are frequently themselves acted on by their own secretion, and to 

 such an extent, that a perforation of considerable size may be produced, 

 and the contents of the stomach may in part escape into the cavity of 

 the abdomen. This phenomenon is not unfrequently observed in post- 

 mortem examinations of the human body. If a rabbit be killed during 

 a period of digestion, and afterwards exposed to artificial warmth to pre- 

 vent its temperature from falling, not only the stomach, but many of 

 the surrounding parts will be found to have been dissolved (Pavy). 



From these facts, it becomes an interesting question why, during life, 

 the stomach is free from liability to injury from a secretion which, after 

 death, is capable of such destructive effects? 



It is only necessary to refer to the idea of Bernard, that the living 

 stomach finds protection from its secretion in the presence of epithelium 

 and mucus, which are constantly renewed in the same degree that they 

 are constantly dissolved, in order to remark that, although the gastric 

 mucus is probably protective, this theory, so far as the epithelium is 

 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 afterwards, no sign of 

 digestion of the stomach was visible. " Upon one occasion, after remov- 

 ing the mucous me'mbrane, 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 whilst digestion was being carried on, 

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

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

 the denuded spot had contracted to much less than its original dimen- 

 sions/' 



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 



