MILK. 99 



only the differences this fluid has been found to present under 

 varying normal conditions. Yernois and Becquerel have in- 

 dicated a certain amount of variation at different ages and at 

 different periods in lactation, but they show, at the same time, 

 that the fluid is not subject to changes in its composition suf- 

 ficiently great to influence materially the nutrition of the 

 child. * 



If the composition of the milk be compared at different 

 periods of lactation, it will be found to undergo great 

 changes during the first few days. In fact, the first fluid 

 secreted after parturition is so different from other milk, 

 that it has been called by another name. It is then known 

 as colostrum, the peculiar properties of which will be con- 

 sidered more fully hereafter under a distinct head. As the 

 secretion of milk becomes established, the fluid, from the 

 first to the fifteenth day, becomes gradually diminished in 

 density and in its proportion of water and of sugar, while 

 there is a progressive increase in the proportion of most of 

 the other constituents ; viz., butter, caseine, and the inor- 

 ganic salts. 1 The milk, therefore, as far as we can judge 

 from its composition, as it increases in quantity during the 

 first few days of lactation, is constantly increasing in its 

 nutritive properties. 



The differences in the composition of the milk, taken 

 from month to month during the entire period of lactation, 

 are not so distinctly marked. It is difficult, indeed, to 

 indicate any constant variations of sufficient importance to 

 lead to the view that the milk varies much in its nutritive 

 properties at different times, within the ordinary period of 

 lactation. 



If we except the first few months, the secretion is not 

 found to present any constant variations in density. Yernois 

 and Becquerel found a notable increase in the proportion of 

 solid matters from the first to the third month ; the sugar 

 was increased from the eighth to the tenth month ; the ca- 



1 YERNOIS ET BECQUEREL, Du lait ckez lafemme, Paris, 1853, p. 24. 



