MILK. 



22B 



569. Caseine differs from albumen in not being 

 separated from its solutions by boiling ; in chemical 

 composition they are almost identical, the only dif- 

 ference being that caseine contains no phosphorus. 

 Caseine consists of — 



10,000 



Caseine contains about one quarter per cent, of inor- 

 ganic matter. 



670. Milk, like blood, consists principally of water 

 holding organic matter in solution or suspension ; 

 milk contains caseine, fatty matter, a peculiar kind 

 of sugar, and small quantities of saline substances, 

 particularly phosphate of lime and various alkaline 

 salts. When milk is kept at a certain temperature, 

 it soon begins to change, a portion of the caseine turn- 

 ing into a kind of ferment, commences putrefaction ; 

 this induces an imperfect fermentation of the sugar, 

 and converts it into lactic acid, and this acid by com- 

 bining with the alkali present in the milk, causes the 

 coagulation or separation of the rest of the caseine. 

 Perfectly fresh milk is always feebly alkaline; but it 

 frequently happens that a small quantity of lactic 

 acid is formed almost as soon as it is exposed to the 

 air, which combines with and neutralizes the alkali 

 originally present in the milk. 



