CHEMICAL CONSTITUENTS OF BODY AND FOOD. 41 



drowsiness. The caloric value of two eggs is about twenty calories; 

 about equal to the heat-value of a tumbler of milk. 



MILK. 



Like eggs, milk contains all the elements necessary for the main- 

 tenance of life, and hence it is regarded as a type of alimentary sub- 

 stances and classed as a perfect food. It serves very well as an 

 infant-food. 



The quantitative composition of cow's milk and human milk is 

 as follows, according to Bunge: 



CARBO- 

 PROTEID. FAT. HYDRATE. SALT. 



Cows' milk 3.5 3.7 4.9 0.7 



Human milk . 1.7 3.4 6.2 0.23 



Fig. 6. Specimens of Milk, viewed through the Microscope. (LANDOIS.) 

 M, Milk. C, Colostrum. 



The amount of fat and carbohydrate is nearly the same in both, 

 there being, however, twice as much proteid and nearly three times 

 as much salt in cows' milk as in human milk. To bring cows' milk 

 to the same condition as human milk, it is necessary to dilute with an 

 equal amount of water, and, at the same time, to add some cream and 

 sugar. 



Milk is a watery solution of various proteids, a carbohydrate and 

 salt, containing in suspension emulsified fat. Cows' milk is an 

 opalescent solution, with a characteristic taste and an amphoteric 

 reaction. The specific gravity varies between 1028 and 1034. Micro- 

 scopically, it consists, like blood, of plasma and corpuscles, or glob- 

 ules, of fat. Boiling does not coagulate fresh milk, but forms a skin 



