THE GASTRIC JUICE. 213 



insisted on by Borelli, and the Florentine academicians, and 

 which he had himself well studied in the graminivorous birds, 

 is replaced by the action of a digestive fluid. 



His ingenious experiments, soon followed by those of 

 Spallanzani, showed that the gastric juice is the solvent of 

 food in the stomach. These observers obtained gastric juice 

 by causing birds to swallow portions of sponge attached to 

 a string, and withdrawing them after a certain time ; by ex- 

 pressing them they obtained a small quantity of gastric juice. 



Spallanzani's experiments proved the solvent action 

 of the gastric juice completely. He caused animals to 

 swallow meat enclosed in metallic spheres, pierced with holes 

 so as to allow the contact of the gastric juice; and, on with- 

 drawing these spheres from the stomach, he found their con- 

 tents partially or wholly digested. 



During the period of fasting, the stomach is empty, and 

 its mucous membrane is pale and covered with a grayish 

 mucus; when food enters it, however, the capillaries become 

 congested, and a liquid exudes like sweat, from the open 

 mouths of the gastric follicles this is the gastric juice. 

 These phenomena, first described by Dr Beaumont, have been 

 repeatedly observed since then in dogs with gastric fistuke. 

 The gastric juice is a clear and transparent liquid, of 

 decidedly acid reaction. Its specific gravity is about 1003'3. 

 If gently heated it possesses the property of gradually dis- 

 solving albuminoid substances, but if the heat be elevated to 

 160, the action is entirely arrested; the reason of this we 

 shall presently investigate. The gastric juice contains 99 per 

 cent, of water, besides certain acids and salts, and a peculiar 

 and very remarkable organic substancer called pepsine; the 

 chemical constitution of each of these substances we shall 

 now shortly pass under review, examining the present 

 doctrines as to their action on the constituents of food. 



