FOODS 31 



Fats and oils. Fats and oils form a part of the composition 

 of plants and animals. Examples of food containing fat are : 

 butter and cream, oils from nuts and olives, and fat from animals. 



Proteins. Proteins contain the element nitrogen in addition 

 to carbon, hydrogen, and oxygen of the carbohydrates and fats 

 and oils. They include some of the most complex substances 

 known to the chemist, and, as we shall see, have a chemical com- 

 position very similar to that of living matter. Proteins occur in 

 different substances. White of egg, lean meat, beans, and peas 

 are examples of substances composed largely of proteins. 



Vitamins. Vitamins, substances the composition of which is 

 practically unknown as yet, are also necessary parts of a diet. 

 We shall learn more about them in Unit XL 



Inorganic nutrients. Water and various salts, some of which, 

 as calcium found in drinking water, form important parts of the 

 diet of plants and animals. Later we shall see that green plants, 

 although they use precisely the same nutrients (carbohydrates, 

 oils, and proteins) as we do, take into their bodies the chemical ele- 

 ments from which these are formed. From these raw food ma- 

 terials organic foods are manufactured in the body of the plant. 



The tree. Foods in a fluid form are circulated to all parts of 

 a tree. It grows by elongating its roots and its branches, and 

 by putting on a thin layer of living matter on all parts of its body. 

 This layer grows more in summer than in winter. If we 

 should cut down a tree, we can see the concentric rings in its 

 trunk which mark its yearly growth. How did the tree do this? 

 Here again the chemical laboratory is at work. The organic 

 foods which were made consist of the same elements that are 

 found in the living stuff of the tree. These foods were used, not 

 only to supply energy so that the tree may do work, but they 

 give it the materials out of which to build its living material. 



Self-Testixg Exercise 



A nutrient is anything that supplies (1\ and (2) or 



(3) up the (4) of living things. Foods are made up of 



(o) and (6). The organic nutrients are (7) , 



:' (8) or (9), and (10). 



