10 Milk and Its Products 
they can be reabsorbed, and portions of partially 
broken down cells break away from the walls of 
the follicle and appear in the colostrum. Gradually 
the colostrum takes on the character of normal 
milk, and in the course of four or five days the 
change is complete. Other characteristics of colos- 
trum are discussed in detail in the next chapter. 
While maternity is the prime cause of secretion, 
it is not the only means of stimulation to the ac- 
tivity of the udder, nor is it a necessary prerequisite 
to the secretion of milk. The regular removal 
of the saline fluid in the gland of the virgin 
animal, or even the stimulation of the organ by the 
friction of the hand or the suckling of a calf, may 
be sufficient to cause the secretion of milk of nor- 
mal character in considerable quantities. In the 
same way and under the same exciting causes, other 
glands of the body, notably the lymphatics in the 
arm pits and the rudimentary mamme of males, 
have been known to secrete a fluid resembling milk 
in all essential characteristics. 
Amount and duration of flow.—With wild ani- 
mals in a state of nature, the milk is secreted only 
in amount sufficient for the needs of the young 
animal, and only until the young is sufficiently de- 
veloped to secure its food independently of the 
mother. Under the influence of domestication the 
cow has been brought to increase her flow of milk 
many fold, and the time during which it is se- 
ereted has been lengthened until it is almost, and 
indeed is, in some cases quite continuous. A dis- 
