THE SECRETION AND PROPERTIES OF MILK 1293 



Bunge. The following Table shows the composition of the ash of a rabbit 

 fourteen days old, of the milk which it was receiving from its mother, of 

 the ash of rabbit's blood and blood serum. Nothing could be more striking 

 than the marvellous way in which the cells of the mammary gland have 

 picked out from the salts of the circulating plasma exactly those salts which 

 are needed for the growing animal and in the same proportion : 



This close correspondence is necessary only where growth is very rapid, 

 so that the greater part of the constituents of the milk have to be utilised 

 in the building up of the animal tissues. As Bunge has shown, the slower 

 the growth of the animal the greater the divergence between the composition 

 of the milk and that of the new-born animal. We may compare for instance 

 the rabbit, which doubles its weight in six days, with the dog, which doubles 

 its weight in ninety-six days, and the human infant, which takes one hundred 

 and eighty days to double its weight at birth. 



The last column of the following Table represents the composition of the 

 ash of cow's milk, and shows how very inefficiently this milk can be regarded 

 as replacing human milk, the natural food of the infant. 



The relation between rate of growth and protein content of food is well 

 illustrated by a comparison of the composition of the milk in different 

 animals. In the following Table (Proscher) it will be seen that the more 

 rapidly an animal grows the greater is the protein content of the milk with 

 which it is supplied : 



