148 EGGS. 



States Department of Agriculture. Incidentally we would call 

 attention to these publications, which are issued free or at a 



FIG. 91. Mammary gland of dog, showing the formation of the secretion: 

 A, medium condition of growth of the epithelial cells; B, a later condition (after 

 Heidenhain). 



nominal cost by the Government, and are full of practical value, 

 not alone to farmers, but to all students of economics. 



EGGS. 



Eggs in various forms enter largely into the common dietary. 

 So far as birds are concerned, eggs may be regarded as a perfect 

 food, inasmuch as until the young leaves the shell all its nutrition 

 has been obtained from the shell and its contents, together with 

 what it has obtained from the atmosphere. 



The egg of the hen is the one commonly used as food, although 

 ducks' eggs are eaten to a considerable extent. In a hen's egg 

 weighing 50 grams there are 7 grams of shell, 27 grams of the 

 white, and 16 grams of yolk. The yolk and white are made 

 up of water, 73.5; proteids, 13.5; fats, 11.6 ; and salts, 1 per 

 cent. 



The white of egg consists of egg-albumin, egg-globulin, and 

 ovoniueoid, with some sugar, fat, lecithin, cholesterin, and salts. 



The yolk is composed of two kinds of material, one yellow, 

 containing fat and the yellow coloring-matter lipochrome, and the 

 other nearly white in color in which is found the nucleoproteid, 

 vitellin, together with sugar, lecithin, cholesterin, and salts, as in 

 the white. 



The white of the egg in its raw state is more digestible than 

 when cooked, but there are few persons to whom raw eggs are 

 palatable. Egg-albumin is coagulated at a temperature of 73 C., 

 and vitellin at 75 C. When the temperature reaches 100 C., the 

 boiling-point, and is kept there for some time, the albumin is so 

 thoroughly and densely coagulated as to be difficult of digestion. 



Eggs have a high nutritive value, being so rich in proteid con- 

 stituents, but must be supplemented by carbohydrates, in which 

 they are very deficient. They contain no free purin or purin- 

 yielding bodies (p. 434), and are therefore useful when a diet free 



