xi] MILK AS A FOOD 169 



in different foods varies very considerably, and that 

 the feeding value of a food should never be solely 

 estimated by simply taking into account the per- 

 centages of the different nutrients it contains. 



Value of Milk as a Food.^-If we examine the 

 composition of milk, in the light of the above neces- 

 sarily brief statement of the nature and functions of 

 the different food nutrients, we shall find why it 

 should occupy such a unique position among foods. 

 In the first place, it contains no refuse portion ; and, 

 in the second place, it contains members of all the 

 different groups of nutrients. The albuminoids are 

 represented by casein and lactalbumin, which amount 

 to, on an average, 3 J per cent ; the fats are represented 

 by butter-fat, which amounts to 3f per cent ; while 

 the carbohydrate group is represented by the milk- 

 sugar, averaging about 4J per cent ; and, lastly, we 

 have in the ash the necessary mineral ingredients. 



Digestibility of Milk. With regard to the digesti- 

 bility of these food nutrients in milk, broadly speaking, 

 it may be said that, so far as the small number of 

 experiments, carried out on this subject, go to show, 

 all the protein and all the carbohydrates are digested. 

 The same, however, is not the case with the fat, 

 which, it would seem, is only digested to the extent 

 of about 96 per cent. In cheese, again, the same 

 may be said, the fat being slightly less digestible, 

 viz. to the extent of 95 per cent. In butter, however, 



