HUMAN POODS. 



165 



XII. HUMAN FOODS. 



COMPOSITION OF HUMAN FOOD MATERIALS.* 



(Atwater.) 



Ordinary food materials, such as meat, fish, eggs, pota- 

 toes, wheat, etc., consist of — 



Refttse. — As the bones of meat and fish, shells of shellfish, 

 skin of potatoes, bran of wheat, etc. 



Edible Portion. — As the flesh of meat and fish, the white 

 and yolk of eggs, wheat flour, etc. The edible portion con- 

 sists of water and 7iutritive ingredients or nutrients. 



The principal kinds of nutritive ingredients are protein, 

 fats, carbohydrates, and mineral matters. 



The water, refuse, and salt of salted meat and fish are 

 called non-nutrients. In comparing the values of different 

 food materials for nourishment they are left out of account. 

 Classes of Nutrients. — The following are familiar examples 

 of compounds of each of the four principal classes of nutri- 

 ents 



{ Albu7ninoids, e.g., albumen (white of 

 I eggs); casein (curd)of milk; myosin, 

 j the basis of muscle (lean meat) ; 

 Proteids. \ gluten of \yheat, etc. 



Gelatinoids, e.g., collagen of tendons; 

 ossein of bones; which yield gelatin 

 Protein.^ t or glue, etc. 



Meats and fish contain very small quantities of 

 so-called 'extractives." They include kreatin 

 and allied compounds, and are the chief ingre- 

 dients of beef-tea and meat-extract. They 

 contain nitrogen, and hence are commonly 

 classed with protein. 

 Fats, e.g., fat of meat ; fat (butter) of milk ; olive-oil ; oil 



of corn, wheat, etc. 

 Carbohydrates, e.g., sugar, starch, cellulose (woody fiber), 

 etc. 



* Extracts from " Foods, Nutritive Value and Ccot " ( Farmers' Bulletin 

 No. 23), and " Food and Diet " (,U. S. Dept. of Agriculture Year book, 1894). 



