DIGESTION. 



253 



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 sympathetic 

 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 ref- 

 erence. 



Digestion of the Stomach after Death. If an animal die dur- 

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

 gastric juice is present in the interior of the stomach, the walls of this 

 organ itself are frequently themselves acted on by their own secretion, 

 and to such an extent, that a perforation of considerable size may be pro- 

 duced, 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 afterward exposed to artificial warmth 

 to prevent 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 eifects? 



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 con- 

 cerned, 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 digestion of 

 the stomach was visible. '"Upon one occasion, after removing the mu- 

 cous 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 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 con- 

 tracted to much less than its original dimensions." 



Pavy believes that the natural alkalinity of the blood, which circulates 

 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 secre- 

 tion is quite sufficient to destroy its digestive powers; but the experi- 



