in] THE CONSTITUENTS OF MILK 29 



through, like the other albuminoids, which are in 

 true solution. The presence of this glue-like caseous 

 matter in milk exerts an important influence on the 

 state of the fatty globules, as we shall see later on, 

 by preventing the more minute ones from separating 

 out from the main body of the milk by rising to its 

 surface. The caseous matter of rnilk may be regarded, 

 then, as being of the nature of a salt, in which the 

 casein proper takes the part of the acid, and the 

 lime that of the base. The proportion in which 

 the casein and lime are respectively present are 100 

 parts of the former to 1'55 of the latter. As we 

 shall see farther on, the action of rennet or dilute 

 acids is to decompose this caseous matter, and to 

 precipitate it from its colloidal form into an insoluble 

 one. 



The caseous matter in its semi-dissolved condition 

 possesses a certain amount of opacity. The opacity 

 of milk is, therefore, due to its caseous matter as well 

 as to its fatty globules. This is seen from the fact 

 that creamed milk, which contains as little as '1 per 

 cent of fat, presents considerable opacity. It is this 

 body which forms the chief constituent of the curd 

 or coagulum of milk, the nature of which, according 

 to the conditions under which it is produced, will be 

 discussed when dealing with cheese. 



It has been noticed that, when milk is allowed to 

 stand for some time, an alteration of the casein into 



