126 



FOOD. 



Meat ; . i 5 to 10 per cent. 



Milk ....... 3 to 4 " " 



Eggs 12 " 



Cheese 8 to 30 " " 



Butter '- -^ 85 to 90 u " 



Proteids. This class contains some of the most valuable of 

 the food-stuffs. The importance of the class is readily understood 

 when it is recalled that the principal ingredients of the blood and 

 the muscles are supplied by the proteids of the food. This is the 

 only class whose members contain nitrogen, and it has therefore 

 been sometimes spoken of as the " nitrogenous " class. The albu- 

 minoids contain nitrogen also, but this class has little nutritive 

 value, except gelatin, which is valuable, but, as has already been 

 stated, its nitrogen is not available for tissue-forming. The proteids 

 are represented in eggs by albumin, in milk by casein, in meat by 

 myosin, in peas and in beans by legumin, and in the cereals by 

 gluten. The amount of proteids varies in different foods ; thus 

 there is in 



Meat 15 to 23 per cent. 



Milk 3 to 4 



Peas and beans 23 to 27 



Grains (flour) 8 to 11 



Bread 6 to 9 



Potato 1 to 4 



The following diagram (Fig. 85) shows the amount of the 

 principal food-stuffs in some of the more generally used foods : 



Proteids. 



Fats. Carbohydrates. Water. 



Explanation 



Bread 



FIG. 85. Diagram showing proportion of the principal food-stuffs in a f w 

 typical comestibles. The numbers indicate percentages. Salts and indigestible 

 materials omitted (after Yeo). 



