204 DIGESTION. [CHAP. xxiv. 



of 98 or 100; afterwards add dilute muriatic acid to the fluid 

 until it redissolves the precipitate which is at first thrown down ; 

 the fluid thus formed will be found to possess full digestive powers, 

 and all the properties of the gastric fluid. It is, in fact, an acidu- 

 lated solution of pepsine in water. The pepsine may be precipi- 

 tated from this solution by some of the reagents which coagulate 

 albumen. Bichloride of mercury will do this, and render the fluid 

 inert. Alcohol and water at the boiling temperature produce the 

 same effect : the precipitate, however, thrown down by alcohol, is 

 capable of being redissolved in water, and then, with acid, will 

 produce a digestive fluid. Tannin also precipitates it. It is evi- 

 dent, therefore, that the digestive fluid contains a principle capable 

 of affording distinct reactions. The solvents of this principle are 

 water and dilute muriatic or acetic acids. 



The power which the digestive fluid has of coagulating caseine, 

 independently of its acid, denotes that it holds in solution some 

 special agent derived from the mucous membrane of the stomach. 



Alcohol added to a fresh infusion of mucous membrane throws 

 down a white flocculent precipitate, which may be collected on a 

 filter, and when dried will produce a grey compact mass. This, 

 when redissolved in water, will exhibit digestive powers ; and these 

 powers are greatest when it is united with acetic and muriatic 

 acids. We obtain in this way the nearest approach to the isola- 

 tion of pepsine. 



The Acid of the Gastric Juice. Of the existence of an organic 

 principle, a secondary organic compound, the product of the secre- 

 tory action of the mucous membrane of the stomach, no doubt can 

 be entertained ; but we can speak with less certainty of the nature 

 of the acid which exists along with it in the gastric fluid of the 

 stomach, inasmuch as recent observers have thrown a doubt upon 

 the correctness of Prout's opinion. The following are the most 

 recent opinions put forward on this subject. 



Blondlot affirms, that the acidity of the gastric juice is due not 

 to the presence of a free acid, but to the existence of biphosphate 

 of lime as one of its ingredients. To this, however, Melsens and 

 Dumas raise the objection, that carbonate of lime, or Iceland spar, 

 placed in gastric juice for some hours, becomes corroded and suffers 

 a very notable diminution of weight, which can arise solely from 

 the presence of a free acid. MM. Bernard and Barreswil likewise 

 state some strong objections to the views of M. Blondlot, in a 

 paper published in 1844. They show that M. Blondlot failed to 

 obtain effervescence by adding carbonate of lime to gastric juice. 



