MILK AS A FOOD 53 



percentage of fat. This is due to the opacity of the casein 

 which is present in greater proportion in cow's milk. 



Both milks are amphoteric or slightly alkaline in reac- 

 tion when freshly drawn, but cow's milk is practically 

 always acid when used under ordinary circumstances. 



Cow's milk contains about four times as much inorganic 

 salts as woman's milk. The composition of these salts, 

 furthermore, varies markedly. In cow's milk the alkaline 

 earths, such as lime and magnesia, predominate, while in 

 woman's milk the alkaline bases, such as potassium and 

 sodium, predominate. These differences have an import- 

 ant bearing upon infant feeding. 



The amounts of fat in the two milks do not differ mark- 

 edly. There is a difference in the composition of the fat. 

 Woman's milk contains much more cholesterin, a fatty 

 body, than cow's milk. 



The sugar in the two milks varies markedly in amount, 

 but not in kind. The milk sugar in both cases is in com- 

 plete solution. 



One of the chief differences between cow's milk and 

 woman's milk lies in the proteins. Cow's milk contains 

 4.5 per cent, while woman's milk contains only 1.5 per 

 cent. The reason for this is that the ratio of the growth of 

 the caff, compared to that of the infant, is about as 2 to 1. 

 Further, the protein of cow's milk consists chiefly of casein 

 and little lactalbumin, while the protein in woman's milk 

 contains more lactalbumin and less casein. For this reason 

 the curd which separates out from cow's milk consists of 

 tougher and larger masses than the curd from woman's 

 milk. 



The antibodies and other protective substances also differ 

 in the two milks. 



Man has but a single stomach and this forms about 

 twenty per cent of the digestive tract. The cow has four 

 stomachs which form about seventy per cent of the diges- 

 tive tract. The caff's stomach is well fitted to handle and 





