COMPOSITION OF MILK. 15 
albuminoids in milk. But after these two have been separated 
from milk a slight precipitation can be obtained by treating 
the filtrate with alcohol. This has been called albumose and 
also lactoglobulin. From this resultant filtrate can again 
be separated a very small amount of material containing 
nitrogen. Dr. Babcock has obtained a substance from milk 
called fibrin. These latter substances, however, are present 
in minute portions, and are believed by some of the best scien- 
tists to be the same as the albumen, and their presence in the 
filtrate is due to incomplete precipitation of the albumen in 
the first place. 
Casein.—Casein is by far the most important of all of the 
albuminoids. It is the substance which forms the curd in 
cheese-making. In fresh milk, as is now understood, it is in 
chemical combination with lime salts. It is on this account 
that fresh milk shows the amphoteric reaction, which will be 
explained under the “ Properties of Milk.” The coagulation 
of casein by the addition of rennet or dilute acids is thought 
to be due to this union between the casein and lime. Fleisch- 
mann refers to this as the ‘‘ caseous matter” of milk. The 
viscosity of normal milk is believed to be due in a large meas- 
ure to this condition of casein in milk. It causes the casein 
to be present in a colloidal condition. When milk coagu- 
lates by natural or by artificial means, the union between 
the casein and lime phosphate is largely broken. 
Casein and albumen differ in composition, in that the casein 
contains phosphorus and less sulphur than does albumen. 
Fleischmann maintains that a substance called nuclein is 
associated with casein, and is not found in albumen. 
Casein is precipitated by the use of rennet and dilute acids, 
and coagulates spontaneously, due to the acid formed in the 
milk. The precipitates formed by the use of different pre- 
cipitating agents are not alike. The curd coagulated by ren- 
net contains more fat and calcium phosphate than the curd 
does which is precipitated by dilute acid or soured sponta- 
neously. If milk stands at air temperature for any length 
