DIGESTION OP FOOD. 323 



ter were concerned in the secretion of the acid of the stomach, 

 but this is by no means certain. Possibly these, like the demi- 

 lune cells of the pancreas, may be the progenitors of the central 

 (chief) cells. The latter certainly secrete pepsin, and probably 

 also rennet. Mucus is secreted by the cells lining the neck of 

 glands and covering the mucous membrane intervening be- 

 tween their mouths. The production of hydrochloric acid by 

 any act of secretion is not believed in by all writers, some hold- 

 ing that it is derived from decomposition of sodium chloride, 

 possibly by lactic acid. So simple an origin is not probable, not 

 being in keeping with what we know of chemical processes 

 within the animal body. 



Self-Digestion of the Digestive Organs.— It has been found, 

 both in man and other mammals, that when death follows in a 

 healthy subject while gastric digestion is in active progress 

 and the body is kept warm, a part of the stomach itself and 

 often adjacent organs are digested, and the question is con- 

 stantly being raised. Why does not the stomach digest itself 

 during life ? To this it has been answered that the gastric 

 juice is constantly being neutralized by the alkaline blood ; 

 and, again, that the very vitality of a tissue gives it the neces- 

 sary resisting powers, a view contradicted by an experiment 

 which is conclusive. If the legs of a living frog be allowed 1 

 to hang against the inner walls of the stomach of a mammal 

 when gastric digestion is going on, they will be digested. 



The first view (the alkalinity of the blood) would not suffice ' ' 

 to explain why the pancreas, the secretion of which acts best in : 

 an alkaline medium, should not be digested. 



It seems to us there is a good deal of misconception about 

 the facts of the case. Observation on St. Martin shows thati 

 the secretion of gastric juice runs parallel with the need of it, 1 

 as dependent on the introduction of food, its quantity, quality, 

 etc. Now, there can be little doubt that, if the stomach were , 

 abundantly bathed when empty with a large quantity of its 

 own acid secretion, it would suffer to some extent at least. But 

 this is never the case ; the juice is carried off and mixed with 

 the food. This food is in constant motion and doubtless the 

 inner portions of the cells, which may be regarded as the dis- 

 charging region (the outer, next the blood capillaries, being 

 the chief manufacturing region of the digestive ferment), are 

 frequently renewed. 



Such considerations, though they seem to have been some- 



