MILK AS A FOOD 45 



small quantities of magnesia and traces of oxide of iron in 

 combination with phosphoric acid, chlorine, and sulphuric 

 acid. 



The amount and nature of the inorganic salts vary con- 

 siderably in the milks from different animals. Cow's milk 

 contains almost four times as much inorganic salts as wo- 

 man's milk. Thus cow's milk contains 0.75 per cent, while 

 woman's milk only 0.2 per cent. When we examine the 

 nature of these salts we find still greater differences, for the 

 inorganic salts in woman's milk consist mainly of the 

 alkaline bases, potassium and sodium, whereas the inor- 

 ganic salts in cow's milk consist mainly of the alkaline 

 earths, calcium and magnesium. This difference has an 

 important bearing upon inf ant feeding. One of the reasons 

 why cow's milk sometimes disagrees with babies, upsets 

 their digestions, and results in ill-health is the fact that 

 there is not enough potassium and sodium in the cow's 

 milk which they receive. 



Gases. Certain gases occur in their free state in milk. 

 Freshly drawn milk contains a variable quantity of oxy- 

 gen and always considerable carbonic acid and a slight 

 quantity of nitrogen. Upon standing, the carbonic acid 

 soon escapes and oxygen is absorbed. When milk decom- 

 poses, large quantities of carbon dioxide, as well as other 

 gases, may be formed. 



Enzymes or "life" in milk 



It is commonly supposed that milk is not an inactive 

 liquid, but possesses some indefinable principle or proper- 

 ties which are more or less characteristic of living tissues. 

 Milk, indeed, possesses certain substances common to the 

 blood and other vital liquids, such as antitoxines, opsonins, 

 agglutinins, and other antibodies. Many of the cells in 

 milk are doubtless not dead, and in other ways milk ap- 

 pears to possess " vital " properties. However, it is by no 

 means proper to speak of milk as possessing "life," using 



