CHAP. XXIV.] THE GASTRIC JUICE. 203 



The gastric fluid possesses the property of causing the coagula- 

 tion of the caseine of milk ; an artificial digestive fluid made from 

 the mucous membrane of the true stomach of ruminants possesses 

 the same power, even if its acid be neutralised by potass. This 

 fact has been long known to the makers of cheese ; and the dried 

 mucous membrane of the fourth stomach of the calf has been used, 

 under the name of rennet, for the purpose of coagulating that prin- 

 ciple in milk. That it possesses this power independently of any 

 acid which it may contain, was first pointed out by Berzelius. 

 Some have affirmed, that this power belongs only to the mucous 

 membrane of the stomach of sucking animals. 



A fluid of such digestive power as that above described, cannot 

 be made from any mucous membrane but that of the stomach. 

 The mucous membrane of the bladder, of the greatest portion of 

 the intestinal canal, is quite insufficient for this purpose ; but that 

 of the duodenum appears to exert some solvent influence. 



The Organic Principle of the Gastric Juice. All these facts show 

 that the gastric mucous membrane contains some material which, 

 when dissolved or diffused in acidulated water, exercises a power 

 not to be distinguished from that of the gastric juice itself. Can 

 this material be isolated ? There is no doubt that we can obtain 

 from the mucous membrane of the digestive stomach of animals, an 

 organic substance, which exhibits reactions in close analogy witli 

 those of albumen, and which exercises a solvent or catalytic influ- 

 ence upon various azotised substances ; to this substance Schwann 

 and Miiller gave the name " pepsine" * 



Valentin very justly remarks, that the organic combinations 

 upon which the solvent power of the gastric fluid depends, share 

 the same fate with other contact substances; namely, that they 

 cannot be obtained in perfect purity, nor can their precise relative 

 proportions be determined with exactness. Pepsine, therefore, he 

 adds, can only be regarded as a hypothetical or conventional name 

 for an unknown mass which may be separated by alcohol, or by 

 lead and alcohol in combination with other bodies. Nor do the 

 reagents indicate any definite character they only afford conjec- 

 tural information. To view it as a kind of diastase, whilst it does 

 not remove our difficulty, nevertheless denotes the power of the 

 unknown substance in a more precise and definite manner. 



An artificial digestive fluid may be made in the following man- 

 ner. Let a piece of the mucous membrane of the stomach of a pig 

 be macerated in distilled water for twelve hours at the temperature 

 * Also called g aster ase by French writers. 

 p 2 



