892 THE PHYSIOLOGY OF REPRODUCTION. 



adaptive secretion. This fact is illustrated in the following table 

 giving the mineral constituents in 100 parts of ash: 



YOUNG PUP. DOGS' MILK. DOGS' SERUM. 



K 2 O.. 8.5 10.7 2.4 



Na 2 8.2 6.1 52.1 



CaO 35.8 34.4 2.1 



MgO 1.6 1.5 0.5 



Fe 2 O 3 0.34 0.14 0.12 



P 2 O 5 39.8 37.5 5.9 



Cl 7.3 12.4 47.6 



On account of the use of cows' milk in place of human milk in 

 the nourishment of infants much attention has been given to 

 the relative composition and properties of the two secretions. 

 The chief difference between the two lies apparently in the casein. 

 The casein of human milk is smaller in amount, curdles in looser 

 flocks than that of cows' milk, and seems to dissolve more easily 

 and completely in gastric juice. The former also contains rela- 

 tively more lecithin and less ash, particularly the lime salts. On 

 the other hand, cows' milk contains less sugar and fat. In using 

 it, therefore, for the nutrition of infants it is customary to add 

 water and sugar. The composition of cows' milk is so well known 

 that it is easy to modify it for special cases according to the in- 

 dications. The rules for this procedure will be found in works 

 upon pediatrics. 



