20 BIOLOGY FOR BEGINNERS 



and recombine them into organic compounds, a thing which no 

 animal can do. Nor can we imitate it in any laboratory experiment. 



Though animals use water and some mineral salts, they depend 

 for their life on the organic compounds made by the plants. Flesh- 

 eating animals live on other animals, which in turn use plant food. 

 The fact that plants can use inorganic food, while animals depend 

 on plants for their inorganic nourishment, is one of the most im- 

 portant facts for us to remember. 



Of course the plant forms these organic compounds for its own 

 growth and food, to be stored away by the plant and used when 

 necessary. Whenever we eat a loaf of bread or a piece of candy 

 we are using material the wheat plant or sugar cane had assimilated 

 and would have used as food for itself. 



ORGANIC COMPOUNDS. NUTRIENTS 



Fortunately, the very complicated compounds which the plants 

 provide and which both plants and animals use for food and 

 growth, can be grouped into three great classes called: (1) Pro- 

 teids, (2) Carbohydrates, (3) Fats. These are sometimes taken 

 all together and called organic nutrients. 



Proteids. These are very numerous and are found in all living 

 substances; the following are some that are common and found 

 in large amounts. 



Proteid Where found 



Gluten in grains 



Legumin in peas and beans 



Myosin in lean meat 



Albumen in the white of egg 



Casein in milk and cheese 



It is not necessary to learn these names but the list is put in 

 to show that proteids are of many kinds and, though first provided 

 by plants, are needed in animal tissue as well. 



Test for Proteids. Proteids differ in many ways but there is 

 one point in which they all behave alike and which is different 



