SUMMARY OF CHAPTER III 



ON THE ORGANIC CONSTITUENTS OF MILK 



i. The Proteins. The amount of protein present in milk varies 

 with different species. The protein-content of cows milk is from 

 two to two and a half times as great as that of human milk. 



Two proteins (possibly three) are found in milk caseinogen and 

 lact-albumin. Small amounts of lacto-globulin are probably also 

 found. The separation of caseinogen and lact-albumin from 

 milk can be accomplished without difficulty. Caseinogen is pre- 

 cipitated by acetic acid, or by half saturation with ammonium 

 sulphate, and by other reagents which do not affect the albumin. 

 The separation of caseinogen and of a possible lacto-globulin is 

 more difficult, since caseinogen partakes of the nature of a globulin, 

 and tends therefore to be precipitated by the same reagents. Those 

 investigators who have used chemical methods have differed in their 

 views as to the presence of a true globulin, mainly on these grounds. 



Later work undertaken with biological methods renders it 

 fairly certain that this third protein is present in milk, although 

 in small quantities. From a nutritional standpoint it can almost 

 certainly be neglected, but biologically it is probably of considerable 

 importance. 



The term ' whey-protein ' is frequently applied to the protein 

 of milk apart from caseinogen. This term will include the lact- 

 albumin and the globulin, since caseinogen alone is affected by 

 the curdling with rennet. 



The excess of protein in cows' milk over human milk is mainly 

 due to the larger amount of caseinogen. Lact-albumin appears 

 to be present in human milk in rather larger amount than in 

 cows' milk, although the absolute amount is less than that of the 

 caseinogen. 



Caseinogen contains a good deal of phosphorus, and is combined 

 also with calcium. Lact-albumin is stated to contain a higher 

 percentage of sulphur than caseinogen. Slight differences in 

 composition are obtained between the caseinogen of cows' milk 

 and that of human milk. 



There is no reason to suppose that the proteins of cows' milk 



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