COMPOSITION OF MILK 261 



Frequently, prolongations of mammary tissue extend laterally from the 

 gland toward the border of the axilla, sometimes they are found near the 

 sternum. 



The function of the mammary gland is the secretion of milk. 

 This is a true secretion; the cells of the tubules forming a new sub- 

 stance from materials brought by the blood, which, although not 

 utilized in the body where it is formed, is not only useful but 

 capable of sustaining life. 



Note. The presence and activity of the ovaries seem to be essential to 

 the proper development of the mammary gland. 



Milk is a bluish-white fluid consisting of clear plasma (milk 

 plasma) holding nutritive substances in solution and floating 

 myriads of oil globules, to which it owes its white color. It is a 

 natural emulsion. The variety of nutritive substances contained 

 in it is sufficient for the development of the body of the infant. 



Human milk is amphoteric. 1 



The contained proteins are peculiar to milk and form a soft 

 . flaky curd in the process of digestion. They are several in number, 

 the most important being caseinogen, from which casein is derived 

 in the process of digestion. (Cow's milk forms a tough curd in 

 digesting. It contains more casein but less sugar and less fat. It 

 is nearer acid than human milk.) 



The sugar of milk is lactose (probably absorbed as such does 

 not require digesting). The salts are the various salts found in 

 foods and the body tissues, the most abundant being compounds 

 of calcium, potassium and sodium. 



The water and salts are derived directly from the blood by 

 filtration; the special proteins and lactose are secreted by the cells 

 of the tubules. (Lactose is found nowhere but in milk, the same 

 is true of lact-albumin they are special secretions of the mammary 

 glands.) 



Average percentage of fat, sugar and proteins in milk as given 

 by Holt: 



Colostrum Human milk Cow's milk 



Fats 2.04 3-5 3.5 



Sugar 3. 74 6-7 4-3 



Proteids 5.71 1-2.25 4 



1 Amphoteric. Neither acid nor alkaline, acting on both red and blue litmus 

 paper. 



