34 HANDBOOK FOR BIO-CHEMICAL LABORATORY. 



be kept for several months without decomposition, retaining 

 active proteolytic properties. Such juice does not, however, 

 contain merely acid and pepsin, but considerable quantities 

 of albumoses and peptones. (Gamgee's Phys. Chem., vol. ii., 

 page 82.) 



Milk-curdling Ferment of the Stomach. 



(RENNIN OR CHYMOSIN.) 



Preparation. Cut up five calves' stomachs finely, after 

 washing, and digest the mass for about 24 hours with a 0.5$ 

 common-salt solution, keeping the temperature at about 30 

 0., or less. After digestion filter, measure the filtrate, and 

 acidify with hydrochloric acid, so that it contains 0.1$ of the 

 acid. A thick precipitate of mucous matter is formed, and 

 to facilitate its easy separation the liquid is kept at 20-30 

 C. and allowed to stand until all of the mucous matter has 

 separated, or centrifugal force may be used. Filter, measure 

 the filtrate, and acidify with HC1 again so that the filtrate 

 contains 0.5$ acid, and now add powdered common salt until 

 no more salt dissolves. This supersaturated, acidulated salt 

 solution is brought to a temperature of 25-30 C., and kept 

 at this temperature for 2-3 days, under constant agitation, 

 and then allowed to remain quiet for a day or so, the tem- 

 perature being raised to 30 to 35 C. A flocculent substance 

 is obtained, which rises to the surface of the liquid or is sus- 

 pended therein. This is carefully filtered off, and then dried 

 at a temperature of about 28 0. The product thus obtained 

 is the pure zymotic product.' 



Properties. Rennin or chymosin is an amorphous, white, 

 gelatinous substance, greatly resembling aluminium hydrate. 

 It is without taste or smell, soluble in water, forming a limpid 

 or clear solution. Chymosin has the property of curdling 

 large amounts of milk at 37 C., or pure casein solutions 

 containing calcium salts, 



