HOME ECONOMICS AND EDUCATION 539 



proportions. In some cases material which is edible is classed as re- 

 fuse because the flavor is objectionable, as peach and plum pits 

 commonly thought to be actually injurious. 



FOOD AS BUILDING MATERIAL AND FUEL. 



Blood and muscle, bone and tendon, brain and nerveall the 

 organs and tissues of the body are built from the nutritive ingredi- 

 ents of food. With every motion of the body and with the exercise 

 of feeling and thought as well, material is consumed and must be 

 resupplied by food. In a sense, the body is a superior machine. 

 Like other machines, it requires material to build up its several 

 parts, to repair them as they are worn out, and to serve as fuel. 

 The steam engine gets its power from fuel ; the body does the same. 

 In the one case coal or wood, in the other food, is the fuel. In both 

 cases the energy which is hidden in the fuel the potential energy, 

 as it is called in scientific language is transformed into power 

 and heat. 



From the time foods are taken into the body until they are 

 digested, absorbed, utilized, and finally converted largely into the 

 carbon dioxid and water vapor of the breath and the nitrogenous 

 and other excretory products of the urine and feces, they undergo 

 great chemical changes, very many of which liberate heat as a re- 

 sult of oxidation or some closely related process. It is through these 

 complex chemical processes that the body derives the energy for in- 

 ternal and external muscular work. Heat is evolved by such chemi- 

 cal changes and also results from the muscular work of the body. 



The amount of heat produced in the body must, of course, 

 vary with the amount of food eaten, the work done, and other cir- 

 cumstances. However, the body is such a perfect piece of mech- 

 anism that the loss of heat by radiation, etc., is so adjusted to 

 heat production that body temperature remains fairly constant. 

 In the use of its source of power the body is much more economical 

 than any engine. But the body is more than a machine. It has 

 not simply organs to build and keep in repair and supply with en- 

 ergy; it has a nervous organization; it has sensibilities; and there 

 are the higher intellectual and spiritual faculties. The right ex- 

 ercise of these depends upon the right nutrition of the body. 



The chief uses of food, then, are two: (1) To form the mate- 

 rial of the body and repair its wastes, and (2) to furnish muscular 

 and other power for the work the body has to do and yield heat to 

 keep the body warm. In forming the tissues and the fluids of the 

 body the food serves for building and repair. In yielding power 

 and heat it serves as fuel. If more food is eaten than is needed, 

 more or less of the surplus may be and sometimes is stored in the 

 body, chiefly in the form of fat. When the work is hard or the 

 food supply is low the body draws upon this store of fat and grows 

 lean. 



Protein a Building Material. The principal tissue formers 

 are the protein compounds, especially the albuminoids. These make 

 the framework of the body. They build up and repair the nitrogen- 



