HOME ECONOMICS AND EDUCATION 543 



beverages, such as tea, coffee, cocoa, fruit juices, cider and wines. 

 Animal food, in its initial form, is the flesh of such animals as are 

 accounted suitable, the domestic cattle, swine, sheep, goats, poultry, 

 fish, and wild animals or game. Part of these animals are main- 

 tained for their service as producers of milk or producers of eggs, a 

 service which ends when they are converted to meat. The fresh 

 rmlk of cows and the eggs of poultry may be classified as secondary 

 products. The milk manufactured into butter and cheese becomes 

 a product yet another remove from the initial, and eggs are so promi- 

 nently familiar in daily supplies that many forget their secondary 

 relation to the animals that furnish them. In a less emphatic way 

 butter and cheese, from time immemorial, have been closely asso- 

 ciated with the household care of milk as if they were primary 

 supplies. Under the head of fish are classed fish, mollusca (oysters, 

 clams, etc.), crustaceans (lobsters, crabs, shrimp) and reptiles (tur- 

 tles being the most important). 



The minerals used by the body are not energy producers, but 

 are as necessary to life. Chief among those collected or manufac- 

 tured for human food are salt and to a more limited extent soda. 

 The latter is not ordinarily used for its physiological effect but for 

 its mechanical and chemical effect, as when it combines with an 

 acid and gives off gas, which causes bread or cake to become porous 

 and light and so more digestible and palatable as a food. Other 

 minerals are largely derived from organic sources, that is from ani- 

 mal or vegetable foods. Except as medicines, compounds of iron, 

 sulphur, magnesium, phosphorus and other minerals are seldom, if 

 ever, taken in inorganic form. (Dept. Agr. Bui. 142; Div. of Stat. 

 Bui. 24.) 



NUTRITIVE VALUE OF FOOD. 



How Learned. In order to learn definitely the nutritive value 

 of any food and the energy to be obtained by its use, it is necessary 

 to consider not only its chemical composition but the availability 

 of these elements for the body under different conditions. For in- 

 stance, dried beans contain 22.5% protein and 59.6% carbohydrates, 

 but when the amounts of digestible nutrients are considered it is 

 found that only 17.5% protein and 57.8% carbohydrates are avail- 

 able for body use. Over one-fifth of the protein is not digested and 

 so is lost. So a great many experiments concerning the metabolism 

 of matter and energy in the human body have been made. By metab- 

 olism is meant the chemical and physical changes which take place 

 within the body when food is digested and transferred into living tis- 

 sue of various kinds. Metabolism is the general term given to these 

 changes. The metabolism of food means the changes which the 

 food undergoes within the body and the metabolic products are 

 those new products formed by these chemical and physical changes. 

 Examples of such chemical changes are the transforming of insolu- 

 ble starch of food into a soluble sugar by the action of the saliva 

 in the mouth, the action of the digestive juices of the stomach and 



