196 THE INCOME OF ENERGY 



the suckling calf) to stand twenty-four hours in 

 150-200 c.c. 0.1-0.2 per cent solution of hydrochlo- 

 ric acid. Then neutralize the acid with great care. 1 



Separation of Rennin. The extract just prepared 

 contains pepsin as well as renuiii. The reunin may 

 be separated as follows. The neutralized extract is 

 repeatedly shaken with fresh amounts of magnesium 

 carbonate. The resulting precipitates carry down 

 almost all the pepsin and very little rennin. The 

 filtrate still rapidly coagulates milk, but contains only 

 traces of pepsin. This nitrate is now precipitated 

 with lead acetate, the precipitate is decomposed with 

 very dilute sulphuric acid, and the mixture filtered. 

 To the filtrate, which contains the rennin, is added a 

 solution of stearin soap in water. Thereupon the 

 soap is thrown out of solution and falls, carrying the 

 rennin with it. The soap is then removed by shaking 

 with ether, and the rennin remains. 2 



Precipitation of Casein. Add 1 c c. of the 

 neutral extract to 25 c.c. fresh milk at 36-38 C. 

 (Normal milk is amphoteric. If the reaction 

 be acid, the acid should be very carefully 

 neutralized.) 



In a few minutes the milk will separate into 



1 Haramarsten : Upsala Lakareforenings Forhandlingar, 1872, 

 viii, pp. 63-86. Abstract by author in Maly's Jahresbericht 

 iiber die Fortschritte der Thierchemie, 1872, ii, pp. 118-125. 



2 Hammarsten : Lehrbuch der physiologischen Chernie, 1895, 

 p. 241. 



