34 



MILK AND ITS HYGIENIC RELATIONS 



Schryver, to whose book reference should be made for additional 

 information. 



It was found that such separation could be effected by the 

 addition of salts, certain proteins falling out of solution with 

 different salts or with a different concentration of the salt. The 

 two main classes of protein obtained by this means are termed 

 globulin and albumin, the globulin being the more easily pre- 

 cipitated. 



The application of these methods to milk showed that at least 

 two proteins were present in this fluid. Oi these two bodies one 

 was found to belong to the globulin and the other to the albumin 

 group. These substances are known as caseinogen and lact- 

 albumin. Caseinogen is not a true globulin, although it has certain 

 of the properties of the substances of this class. It contains 

 phosphorus, and is probably present in milk as caseinogenate of 

 calcium. 1 



When milk is clotted by means of rennet, caseinogen becomes 

 altered and is known as casein. Caseinogen can be removed 

 from milk by various methods, leaving the rest of the protein in 

 solution. 



Hammarsten thought that a true globulin substance (lacto- 

 globulin) was present in milk in addition to caseinogen, and other 

 investigators have agreed with him. Sebelien (1885) found that 

 a precipitation of lacto-globulin could be obtained when Ham- 

 marsten's method was used, but he gives reasons for doubting 

 whether this can be regarded as a separate substance of globulin 

 type. Halliburton was unable to obtain any evidence of the 

 presence of lacto-globulin. 



It is impossible here to consider fully the literature upon this 

 question, but it seems likely that a third protein body (of globulin 

 type) is present in milk ; normally, however, it occurs in very small 

 quantities. More recently the application of biological methods has 

 appeared to confirm this view, and the amount of lacto-globulin 

 in colostrum appears to be appreciable. 



The small amounts of this substance which have been found 

 in milk render it of comparatively minor importance from the 

 nutritional standpoint, and it is very commonly classed with 

 lact-albumin under the term ' whey-protein.' This term includes 

 the proteins other than caseinogen, which alone of the proteins 

 present in milk is coagulated by the action of rennet. 



On the Amount of Caseinogen and Lact-albumin in Milk. 

 The amount of caseinogen present in cows' milk is much greater 

 than that in human milk, and the higher total protein content of 

 cows' milk may be assigned to this fact. 



Numerous estimations have been made of the caseinogen in 

 both cows' and human milk, and the figures are given in text- 



1 Cp. W. A. Osborne. 



