36 Milk and Its Products 
secure and digest food of the same kind and nature 
as its parents. The function of milk secretion in all 
such animals, then, begins when the young is born, 
increases rapidly for a few days or weeks, as the 
developing infant requires more food, and then grad- 
ually diminishes as the infant with continued growth 
begins to seek its natural and permanent food, and 
finally entirely ceases when the young is able to get 
its own subsistence, at the age of a few weeks in the 
case of most small animals, and in no event longer 
than a few months even with the largest forms. 
The cow the only commercial milk producer.—His- 
tory does not tell us how the cow came to be devel- 
oped as the preéminent producer of milk for man’s 
use. In all probability the milk of the goat and the 
ass was used by man before that of the cow. But 
in her development the cow has shown herself to be 
so much more adaptable to the commercial production 
of milk as to have distanced all other animals in this 
respect. There is no historical evidence that leads 
one to believe that in her wild state the cow had any 
greater tendency to give milk in excess of the demands 
of her offspring or for longer periods of time than 
many other animals. The domestication of the cow 
has resulted in developing an animal in which the 
capacity for secretion has been multiplied many times, 
and the duration of secretion has been made practi- 
eally continuous. As a liberal estimate, a vigorous 
ealf would not need more than 20 pounds of milk per 
day for the first four months of its life, or 2,400 
pounds of milk, and this, or less, would be all that a 
