194 THE INCOME OF ENERGY 



Digestion with Artificial Gastric Juice. Pre- 

 pare three flasks, A, B, and O. In A place 100 c.c. 

 artificial gastric juice ; in B, 100 c.c. 0.2 per cent 

 HC1; and in C, a piece of dried gastric membrane 

 and 100 c.c. distilled water. In each of the three 

 flasks place a small piece of cooked meat, and keep 

 the flasks about five hours at 35-40 C. 1 .Com- 

 pare the result with that observed in natural 

 digestion. 



The artificial gastric juice will digest the meat 

 as did the natural juice in the stomach, but neither 

 the acid alone, nor the mucous membrane free 

 from acid, will digest. There is a ferment in the 

 mucous membrane, but it will not act except in 

 an acid medium. 



Extraction of Pepsin. Pepsin more or less con- 

 taminated with proteid (pepsin may itself be a proteid) 

 may be precipitated from a glycerine extract by alco- 

 hol. 2 The pepsin may also be carried down mechani- 

 cally by an indifferent precipitate as in Brucke's 

 method, 8 in which the mucous membrane, acidulated 

 with phosphoric acid, is allowed to digest until the 

 proteids are mostly converted into soluble peptone. 

 The mixture is then neutralized with lime water. 

 The insoluble calcium phosphate thus formed falls as 



1 Eberle : loc. cit. 



2 Von Wittich: loc. cit., p. 195. 



8 Briicke : Sitzungsberichte der kb'nigliche Akademie der 

 Wissenschaften zu Wien, 1862, xliii, p. 601. 



