MILK. 



695 



phate ; the latter will be acid, because lactic acid has been formed by the 

 fermentation of milk-sugar. 



c. Boil some fresh milk; no coagulum, but a scum is formed. After re-, 

 moval of the scum it is reformed on boiling. Repeat the experiment with 

 milk that has stood some time ; a coagulum is formed. 



Composition. The average composition of various kinds of milk 

 is given below, but it must be remembered that milk not only differs 

 in certain species, but also in the same animal at different times ; 

 for instance, the quality and quantity of food taken, as also various 

 physiological changes, have decided influence upon the milk secreted. 



Human milk. 



Cows' milk. 



The inorganic salts consist chiefly of calcium or sodium phosphate 

 and sodium and potassium chloride, but contain also some magnesium 

 and iron. The proteins consist mainly of casein with some albumin, 

 the proportion being in cows' milk about as 6 to 1, in woman's milk 

 as 3 tc 4. 



Besides the constituents mentioned in the above analyses, milk also 

 contains a very small quantity of extractives, among which are found 

 urea, creatine, lecithin, citric acid, phospho-carnic acid, etc. The 

 principles which give to milk its peculiar odor have not yet been 

 conclusively pointed out. The gaseous constituents of milk are 

 mainly carbon dioxide, oxygen, and nitrogen : 100 volumes of milk 



i Including cane-sugar added by the manufacturer. 



