FERMENTATION 195 



a fine powder carrying the pepsin with it. The precip- 

 itate is dissolved in very dilute hydrochloric acid, and 

 to this solution is added a solution of cholesterin in 

 alcohol and ether. When the two solutions are mixed, 

 the cholesterin separates as an abundant, fine powder 

 bearing the pepsin with it. The cholesterin is removed 

 with ether, leaving the pepsin. 



Ammonium sulphate may also be nsed as the me- 

 chanical precipitant. 1 



Change of Froteid to Peptone by Pepsin. 1. 



Place in a test-tube five drops of the glycerine 

 extract of pepsin witb 5 c.c. 0.2 per cent hydro* 

 chloric acid and a small piece of fibrin. 2 Keep 

 the mixture at 35-40 Cb o 



In a short time the fibrin will be dissolved. 

 Appropriate tests will show that it has been con- 

 verted to peptone. 2. Kepeat the preceding ex- 

 periment, using commercial pepsin (never very 

 free from proteid). 



SPLITTING OF CASEIN BY KENNIN. 



Rennin Extract. Allow the mucous membrane 

 of the stomach (preferably the fourth stomach of 



1 Kiihne and Chittenden: Zeitschrift fur Biologic, 1886, 

 xxii, p. 428. 



2 Preparation of fibrin. With a bundle of smooth rods 

 whip blood as it flows from an artery until the fibrin gathers on 

 the rods. Wash the fibrin in running water until the red cor- 

 puscles are removed and the fibrin shows its natural color. 

 Preserve the fibrin in glycerine. 



