OF MILK i ,. 143 



sufficient to .see and.exarnine^ X 2 ) Casein is sepa-i 

 rated 1 ; ; f rom ; milk :'. . by eentri f ugal force, being dev; 

 posited Jas; .a .film on. the surrounding walls of the; 

 centrifuge. : By whirling milk for a : number;..: :dfe 

 hours, practically all - of the casein can thus be sepa- 

 rated from the milk. It is thus that it is deposited 

 on the walls of the bowl of a centrifugal separator 

 as separator-slime, in which the casein, in a gelat- 

 inous form, is mixed with dirt and other bodies: 

 (3) These two preceding methods of proofs should 

 be sufficiently convincing in regard to the insoluble 

 condition of casein in milk; but the latest method 

 removes all possibility of doubt. Within the past 

 few months, an article has been published .by 

 Kreidl and Neumann, of Vienna, giving results of 

 work done by them in studying milk by what is known 

 as "ultramicroscopic" examination. This method en- 

 ables one to see very much smaller objects than can 

 be seen by the usual methods of microscopic work. 

 These' investigators were able to see the actual par- 

 ticles of casein swimming in milk, to treat 'them with 

 reagents and to observe their various transformations. 

 Their study included the milk not only of cows, but 

 of other animals. , 



Action of acids upon milk^casein.^Milk-casein is 

 madt to appear in milk as : a heavyy white solid or 

 precipitate, in more -or less flocculent form, by means 

 of dilute acids, even by carbon dioxjd under certain 

 conditions, and also by acid salts. .Treatment by 

 acids changes the chemical and . physical properties 

 of milk-casein. The most obvious change is that 

 of physical , condition, the very minute/ invisible 



