94: SECRETION. 



The proportion of water in milk is subject to a certain 

 amount of variation, but this is not so considerable as might 

 be expected from the great variations in the entire quantity 

 of the secretion. In treating of the quantity of milk in the 

 twenty-four hours, we have seen that the influence of drinks, 

 even when nothing but pure water has been taken, is very 

 marked ; and although the activity of the secretion is much 

 increased by fluid ingesta, the quality of the milk is not 

 usually aifected, and the proportion of water to the solid 

 matters remains about the same. 



Nitrogenized Constituents of Milk. Very little remains 

 to be said concerning the nitrogenized constituents of human 

 milk after what has been stated with regard to the compo- 

 sition of cow's milk, in another volume. 1 The different 

 principles of this class undoubtedly have the same nutritive 

 function, and appear to be identical in all varieties of milk, 

 the only difference being in their relative proportion. It is 

 a matter of common experience, indeed, that the milk of 

 many of the lower animals will take the place of human 

 milk, when prepared so as to make the proportions of its 

 different constituents approximate the composition of the 

 natural food of the child. A comparison of the composi- 

 tion of human milk and cow's milk shows that the former 

 is poorer in nitrogenized matters, and richer in butter and 

 sugar ; and consequently, the upper strata of cow's milk, 

 appropriately sweetened and diluted with water, very nearly 

 represent the ordinary breast-milk. 



Caseine is by far the most important of the nitrogenized 

 principles of milk, and supplies nearly all of this kind of 



Zerstzungen. VIRCHOW'S Archiv, Berlin, 1859, Bd. xvii., S. 439. The observa- 

 tions of Hoppe were made upon goat's milk, and in the apparatus used, the milk 

 was drawn directly into the receiver and carefully protected from contact with 

 the air. Hoppe criticises the observations of Lehmann and Vogel as probably 

 incorrect, the fluid not being sufficiently protected from the atmosphere, which 

 gives, according to Hoppe, an excess in the proportion of oxygen. 

 1 Sec vol. ii., Alimentation, p. 77, et seq. 



