THE CHEMICAL CONSTITUENTS OF MILK 317 



that the term has hitherto been used in this book. Cows are 

 particularly suitable for milk production, because, being large 

 animals, they naturally produce large quantities; and the 

 yield has been greatly increased by special selection for many 

 generations. The fact that cattle are reared for beef and may 

 be employed for work is also of importance in this connection. 



The production of milk, however, is not limited to cows. 

 It is the distinguishing character of the class known to 

 zoologists as mammalia perhaps the largest, and certainly the 

 most highly specialised, of vertebrates. 



The milk of all animals contains the same principal 

 constituents as cow's milk. The proportions of these fluctuate 

 in a similar manner, and probably, to a large extent, from 

 similar causes. The average composition of a large number 

 of samples, however, is approximately constant in each. case, 

 and is more or less characteristic of the kind of animal, as will 

 be seen from the following table : l 



AVERAGE COMPOSITION OF MILK OF VARIOUS ANIMALS. 



It will be noted that there is no connection between the 

 size of the animal and the concentration of the milk. On the 

 contrary, as it happens, the milk of the ewe is the most 

 concentrated, and that of the mare the most dilute. In this 

 country, goats are the only animals, other than cows, that are 

 used to any extent for milk production. They are small, hardy 

 animals, and are very convenient for families which could not 

 afford to keep a cow. The composition of goat's milk is very 



1 Konig. 



