COMPOSITION OF MILK. 15 



albuminoids in milk. But after these two have been separated 

 from milk a sHght precipitation can be obtained by treating 

 the filtrate with alcohol. This has been called albumose and 

 also lactoglobuUn. 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 ahke. 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 



