HOME ECONOMICS AND EDUCATION 535 



chemical elements, and hence the two may be discussed together. 

 From fifteen to twenty elements are found, among the most abun- 

 dant of which are oxygen, hydrogen, carbon, nitrogen, calcium, 

 phosphorus, and sulphur. The elements are so combined as to form 

 a great variety of compounds in both body and food. The most 

 important kinds of compounds in the body and in foods are pro- 

 tein, fats, carbohydrates, mineral matter, and water. The functions 

 of these compounds in the food are to build and repair the various 

 tissues of the body and to supply it with heat and muscular energy. 



Water. Water is one of the most abundant of these com- 

 pounds. It forms over 60 per cent of the weight of the average man, 

 being a part of all the tissues. It is thus an important constituent 

 of food, though it can not be burned, and hence does not yield en- 

 ergy to the body. 



Mineral Matter or Ash. Other food ingredients which yield 

 little or no energy and are yet indispensable to the body are the 

 mineral matters. They form only 5 or 6 per cerU of the body by 

 weight, and are found chiefly in the bones and teeth, but are pres- 

 ent also in the other tissues and in solution in the various fluids. 

 When food or body material is burned the mineral constituents re- 

 main as ash. Phosphate of lime, or calcium phosphate, is the min- 

 eral basis of bone. Numerous compounds of potassium, sodium, 

 magnesium, and iron are found in the body and are necessary 

 to life. 



The remaining nutritive materials are organic compounds, so 

 called because they occur principally in the organic, i. e., the animal 

 and vegetable world. They all contain carbon, oxygen, and hydro- 

 gen, in varying proportions. Some also contain nitrogen, phos- 

 phorus, sulphur, or other elements. Those occurring in the body 

 and in food are divided into three principal groups protein, fats, 

 and carbohydrates. 



Protein. This term includes the principal nitrogenous com- 

 pounds-ythose containing nitrogen as one of the elements. Protein 

 is familiar to us in the lean and gristle of meat, the white of eggs, 

 the gluten of wheat, etc. It forms about 18 per cent, by weight, of 

 the body of the average man. Protein compounds may be sub- 

 divided into albuminoids, gelatinoids, and extractives. The albu- 

 minoids include substances similar to the white of egg, the lean of 

 meat, the curd of milk, and the gluten of wheat. The gelatinoids 

 occur principally in the connective tissues, such as the collagen of 

 the tendons and skin and the ossein of bone ; from them is obtained 

 gelatine. 



The albuminoids and gelatinoids, classed together as proteids, 

 are most important constituents of food. They make the basis of 

 bone, muscle, and other tissues, and are essential to the body struc- 

 ture. They are also used as fuel that is, they are burned in the 

 body to yield energy and they are to some extent transformed into 

 fat and stored in the body, but these are their less important uses. 



