vin] RENNET AND ITS ACTION 145 



form of an insoluble clot. Be this as it may, the 

 casein in the milk, to which the term caseinogen has 

 been given, to distinguish it from the casein in the 

 curd, seems to be kept in its state of semi-solution by 

 the alkaline condition of the milk, seeing that the 

 addition of a small quantity of acid at once effects 

 precipitation. 



The action of rennet, however, is much more com- 

 plicated, as it breaks up the casein into two albu- 

 minoid bodies, one of which is easily coagulated by 

 acids, and at a temperature of from 70 to 80 C, 

 (158 to 176 Fahr.) ; whereas the other is not pre- 

 cipitated at all by acids, and is only coagulated by a 

 temperature of from 95 to 100 C. (203 to 212 

 Fahr.). Now it is only the first of these two bodies 

 that is recovered in the curd, since it forms along 

 with alkaline earths a solid body. The second is in 

 solution, and remains in the whey, and is thus lost. 

 According to this theory, then, rennet does not 

 directly possess the power of precipitating the casein 

 in the milk. All that it does is to decompose the 

 casein into two proteid bodies, one of which has the 

 power of becoming coagulated by the calcium salts, 

 which are always present in the milk. This reaction 

 throws some light on the amount of time required 

 for the coagulation of milk by rennet. It may be 

 pointed out, that the amount of albuminoid matter, 

 lost in the coagulation of milk, is further increased 



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