300 SECRETION 



it readily undergoes change into lactic acid in the presence of nitroge- 

 nous ferments, and that it takes on alcoholic fermentation slowly and 

 with difficulty. In the fermentation of milk, the lactose is changed into 

 galactose and dextrose and then into alcohol and carbon dioxide. In 

 some parts of the world alcoholic beverages made from milk are in 

 common use. 



Inorganic Constituents of Milk. It is probable that many inorganic 

 salts exist in the milk, that are not given in the table ; and the separa- 

 tion of these from their combinations with organic matters is one of the 

 most difficult problems in physiological chemistry. This must be the 

 case, for during the first months of extra-uterine existence, the child 

 derives all the inorganic as well as the organic matters necessary to 

 nutrition and development, from the breast of the mother. The re- 

 action of milk depends on the presence of alkaline carbonates, and 

 these are important in preserving the fluidity of casein. It is not 

 determined precisely in what form iron exists in the milk, but its 

 presence here is undoubted. A comparison of the composition of the 

 milk with that of the blood shows that most of the important inorganic 

 matters found in the latter exist also in the milk. 



Carbon dioxide, nitrogen and oxygen exist in solution in milk. Of 

 these gases, carbon dioxide is the most abundant. It is well known 

 that the presence of gases in solution in liquids renders them more 

 agreeable to the taste, and carbon dioxide increases materially their 

 solvent properties. Aside from these considerations, the uses of the 

 gaseous constituents of the milk are not apparent. 



In addition to the constituents given in the table of composition, 

 the milk contains small quantities of nuclein, dextrin, urea, cholesterin, 

 lecithin, hypoxanthin, fluorin and silica. 



A study of the composition of the milk fully confirms the fact that 

 this is a typical aliment and presents in itself the proper proportion 

 and variety of material for the nourishment of the body during the 

 period when development is going on with its maximum of activity. 

 The form in which its different nutritive constituents exist is such that 

 they are easily digested and are assimilated with great rapidity. 

 Human breast-milk is the natural food of the infant. It is immune or 

 partially immune and may confer some immunity on the nursing 

 child. It is bacteriologically pure (Welsh). Passing directly from 

 breast to mouth, it is secure from contamination. It can not be ade- 

 quately replaced by any artificial substitute. 



Variations in the Composition of Milk. If the composition of the 

 milk is compared at different periods of lactation, it will be found to 

 undergo important changes during the first few days. In fact, the first 



