146 ESSENTIALS OF CHEmCAL PHYSIOLOGY 



8. Ringer's method of showing the conversion of caseinogen into casein : — 

 Milk is strongly acidified with acetic acid. This precipitates the caseinogen 

 and entangled fat. The precipitate is collected on a filter, thoroughly washed 

 with distilled water, and ground up in a mortar with calcium carbonate. 

 The mixture is thrown into excess of distilled water. The fat rises to the 

 top : the excess of calcium carbonate falls to the bottom. The intermediate 

 fluid contains the caseinogen in solution ; it is usually very opalescent. Take 

 some of this solution and divide it into three parts, A, B, and C. 



To A add rennet. 



To B add a few drops of 2-per-cent. solution of calcium chloride. 



To C add both rennet and calcium chloride. 



Put all three in the water-bath at 40° C. A clot of casein forms in C, but 

 not in A and B. 



2. The formation of casein from caseinogen is a double process ; the first 

 action is that of the ferment, which converts the caseinogen into what may 

 be called soluble casein ; the second action is that of the calcium salt, which 

 precipitates the casein in an insoluble form, or curd. This is probably a 

 caseate of lime. This may be shown by taking some of Ringer's caseinogen 

 solution and adding rennet. Warm to 40° C. ; no visible change occurs, but 

 nevertheless soluble casein and not caseinogen is now present. Then boil 

 this mixtture to destroy the rennet, cool, and add calcium chloride. A forma- 

 tion of insoluble curd now occurs. 



