88 SECRETION. 



closely studied by Yernois and Becquerel, with reference to 

 their influence upon the composition of the milk ; and their 

 observations will be fully considered in treating of the chem- 

 istry of the mammary secretion. Authors have not noted 

 any marked and constant variations in the quantity of milk 

 in females of different ages. 



Properties and Composition of the Milk. 



The general appearance and characters of ordinary cow's 

 milk are sufficiently familiar and may serve as a standard 

 for comparison with the milk of the human female. 1 Human 

 milk is not so white nor so opaque as cow's milk, having 

 ordinarily a slightly bluish tinge. The milk of different 

 healthy women presents some variation in this regard. After 

 the secretion has become fully established, the fluid possesses 

 no viscidity, and is nearly opaque. It is almost inodorous, 

 of a peculiar soft and sweetish taste, and when perfectly 

 fresh, has a decidedly alkaline reaction. The taste of hu- 

 man milk is sweeter than that of cow's milk. A short 

 time after its discharge from the gland, the reaction of 

 milk becomes faintly acid ; but this change takes place 

 more slowly in human milk than in the milk of most of 

 the inferior animals. 



The average specific gravity of human milk, according to 

 Yernois and Becquerel, is 1032 ; though this is subject to 

 considerable variation, the minimum of eighty-nine obser- 

 vations being 1025, and the maximum, 1046. 2 The observa- 

 tions of most physiological chemists have shown that this 

 average is nearly correct. 



Milk is not coagulated by heat, even after prolonged 

 boiling ; but a thin pellicle then forms on the surface, which 

 is probably due to the combined action of heat and the at- 



1 The properties and composition of cow's milk have already been consid- 

 ered in another volume. See vol. ii., Alimentation, p. 77, et seq. 



2 VERXOIS ET BECQUEREL, Du lait chez lafemme, Paris, 1853, p. 14. 



