FOODS 299 



reasons that the plant does : first, for growth ; second, 

 for the repair of tissues worn out in doing work; 

 and third, for producing heat. For growth we need foods 

 which contain the elements which are found in 

 protoplasm. Heat is produced in the body by slow 

 oxidation. Foods used for this purpose must contain 

 large quantities of carbon, since most of the energy 

 in the body is produced by the oxidation of carbon. 



Foodstuffs. We already know that "we can not live 

 on water, carbon dioxide, and mineral matter from the 

 soil. These simple substances constitute the raw food- 

 materials for plants, but they can not serve as food for 

 us. For our food we use complex chemical compounds 

 in the form of meats and vegetables. Chemists have 

 analyzed our foods, and have found that all of them are 

 composed of one or more of five classes of compounds. 

 These are known as the foodstuffs. The most important 

 foodstuffs are proteins, carbohydrates, fats and oils, 

 minerals, and water. 



Proteins. Different varieties and forms of protein 

 are found in nearly all kinds of animal and vegetable 

 foods. The most common protein foods which we 

 obtain from animals are meat (except fat), milk, eggs, 

 cheese, and gelatin. Of the plants, peas, beans, and all 

 cereals except rice give us protein. 



The proteins are often called the nitrogenous foods 

 because they always contain large quantities of nitro- 

 gen. In addition to nitrogen they contain carbon, 

 hydrogen, oxygen, sulphur, and sometimes phosphorus 



