CONSTITUENTS OF MILK I43 



sufficient to see and examine. (2) Casein is sepa- 

 rated from milk by centrifugal force, being de- 

 posited as a film on the surrounding walls of the 

 centrifuge. By whirling milk for a number of 

 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 

 made to appear in milk as a heavy, white solid or 

 precipitate, in more or less flocculent form, by means 

 of dilute acjds, even by carbon dioxid under certain 

 conditions, and also by aci d salts. Treatment by 

 acids changes the c hemica l and phvsical properties 

 of milk-casein. The most obvious change is that 

 of physical condition, the very minute, invisible 



