222 GENERAL SCIENCE 



simple living as to foods and drink is commonly a sensible 

 manner of life. In these respects as with amusements and 

 recreations the course of life in general should be to reject 

 whatever harms or leads to injury. 



The foods may be grouped sufficiently for our purposes 

 into fats and oils, carbohydrates (such as starch and sugar), 

 and protein foods. Water and certain mineral salts are 

 also considered foods. The fats, oils, starch, and sugar may 

 be regarded as fuels for the body, and source of a large 

 portion of its energy. When they are oxidized the heat 

 liberated maintains the body temperature. The protein 

 foods are largely the tissue-building material. They con- 

 tain the chemical elements carbon, hydrogen, oxygen, 

 and nitrogen, with small quantities it may be of sulphur, 

 phosphorus, and a few other elements. The most familiar 

 foodstuffs rich in proteins are the albumen in eggs, gluten 

 in grains, legumen in beans, myosin in meats, and casein in 

 milk. The chemical composition of some of the proteins 

 is much the same as that of protoplasm into which they are 

 easily changed in the body cells. The carbohydrates cannot 

 be converted into protoplasm. The nitrogen, sulphur, 

 phosphorus, and other elements are obtained by plants from 

 compounds of them in solution in the sap water. Soils 

 deficient in soluble compounds of these elements may have 

 their fertility restored by application of fertilizers containing 

 the necessary chemical compounds. 



A " balanced ration" takes into account the needs of the 

 body for repair and growth, for warmth and energy, and for 

 maintenance of a state of health. It seeks to approximate 

 the relative proportions of the foodstuffs needed by the body 

 at all times, and to vary the proportions to suit the condi- 

 tions of season and employment as these change from time 

 to time. It is impractical to undertake to do more than 

 approximate any exact balance in the foods of which we 



