CASEIN 17 



has obtained a substance from milk called fibrin. These 

 latter substances, howewr. are present in minute portions, and 

 are believed by some of the best scientists to be the :-ame a^ the 

 albumen. Their presence in the filtrate is due to incomplete 

 precipitation of the albumen in the first place. 



Casein. — Casein is In" 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 n(j\v 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 i\Iilk." The coagulation of casein b}' the 

 addition of rennet or dilute acids is thought to be due to this 

 union between the casein and lime. Fleischmann refers to this 

 as the " caseous mailer " of milk. The \'iscosity of n(jrmal milk 

 is believerl to be due in a large measure to this condition of casein 

 in milk. It causes the easein to be present in a coUoiclal condi- 

 ti(jn. \A'hen milk coagulates b_\' natural or by artificial means, 

 the union between the casein and hme phosphate is largeh' 

 broken. 



Casein and albumen difl'er in composition, in that the casein 

 contains phsophorus and less sulphur than does albumen. 

 Fleischmann maintains that a substance called nuclcin is asso- 

 ciated with casein, and is not found in albumen. 



Casein is precipitated b}- the use of rennet and dilute acifls, 

 and coagulates spontaneoush', due to the acid formed in the milk. 

 The precipitates formed b}' the use of different precii)itating 

 agents are not alike. The curd coagulated by rennet contains 

 more fat and calcium phosphate than the curd which is precip- 

 itated b}' dilute acid or by the spontaneous souring of the milk. If 

 milk stands at air temperature for any length of time after milk- 

 ing, the caseous matter (or the nitrogenous matter comljined with 

 lune) tends to separate. The caseous matter of milk is not C(.)m- 

 pletely precipitated by heat, although heat partially destroys the 

 union between the casein and lime. This largel}" destro}.'s the 

 action of rennet. Instead of getting a smooth solifl coagulun-i, a 

 more flaky precipitate is obtained. For this reason milk for 

 cheese-making should not be heated to a high temperature. By 



