MILK. 67 



MILK. 



Milk has a pale blue color, is almost inodorous, of a sweetish taste, an 

 alkaline reaction, and a specific gravity varying from 1.025 to 1.046. 

 Examined microscopically it is seen to contain an immense number of 

 globules, measuring the T o^o"o ^ an ^ 11CQ in diameter, suspended in a clear 

 fluid; these are the milk globules, formed of a small mass of oily matter 

 covered by a layer of albumen. 



The quantity of milk secreted by the human female in 24 hours, during 

 the period of lactation, is about two to three pints; the quantity removed 

 by the infant from a full breast at one time being about two ounces. 



COMPOSITION OF MILK. 



Water 890.00 



Proteids, including casein and serum albumen 35- 



Fatty matter (butter) 25.00 



Sugar (lactose) with extractives 48.00 



Salts..., 2.00 



1000.00 



Casein is the nutritive principle of milk, and constitutes its most import- 

 ant ingredient. It is held in solution by an alkali, but upon the addition 

 of an acid it undergoes coagulation, passing into a semi-solid form. The 

 presence of lactic acid, resulting from a transformation of milk sugar, 

 causes spontaneous coagulation to take place. 



The Fatty matter is more or less solid at ordinary temperature, and con- 

 sists of margarine and oleine; when subjected to the churning process the 

 globules run together and form a coherent mass, the butter. 



When milk is allowed to stand for a varying length of time the fat glob- 

 ules rise to the surface, forming a layer more or less thick, the cream. 



Milk sugar or lactose is an important ingredient in the food of the young 

 child ; it is readily transformed into lactic acid in the presence of nitro- 

 genized ferments. 



Influences modifying the secretion. During lactation there is a 

 demand for an increased amount of fluid, and if not supplied, the amount 

 of milk secreted is diminished. Good food in sufficient quantity is neces- 

 sary for the proper elaboration of milk, though no particular article influ- 

 ences its production. 



Mental emotion at times influences the character of the milk, decreasing 

 the amount of its different constituents. 



Mechanism of Secretion. The water and salts preexist in the blood 

 and pass into the gland vesicles by osmosis. The casein, fatty matter and 



