2 ,- . MANUAL OF MILK PRODUCTS 



For these reasons persistent efforts have been made to domesti- 

 cate animals and develop this function to the highest degree as 

 a source of food for people. 



Wild animals secrete only a sufficient quantity of milk to 

 meet the needs of their young until they become sufficiently 

 developed to secure their own food. Under the influence of 

 domestication the functional activity of the gland has been 

 greatly developed both in the quantity produced and in the 

 duration of the period of lactation. Under domestication the 

 cow in particular has been developed to produce a quantity 

 sufficient to support several offspring and to keep up the secre- 

 tion almost continuously. 



PHYSIOLOGY OF THE MAMMARY GLAND (Bitting) 



The mammary gland being an accessory organ of genera- 

 tion, it is but natural that it should be rudimentary at birth and 

 without function. It remains in this condition until the re- 

 productive function becomes active, at which time it begins to 

 develop quite rapidly and continues to do so until the end of 

 the first period of gestation. Like other organs of the body, 

 it grows with the general growth and also from usage. Its 

 functional activity does not ordinarily begin until near the 

 close of the period of gestation, reaches its maximum at from 

 ten to fifteen days thereafter, and then gradually declines and 

 practically ceases in from six to ten months. If the gland 

 should be examined at birth, a white fluid will be found in the 

 ducts, but it is not true milk. True milk may occur, however, 

 at a very early date and without the stimulus of pregnancy. 



The male is possessed of a rudimentary mammary gland, 

 which does not normally become active but which may produce 

 a fluid closely resembling true milk. 



The udder of the cow consists of two glands lying horizontally 

 side by side and separated by a layer of tissues which helps to 

 support them. The glands are distinct from each other, as 



