220 BIOLOGY 



Hydrocarbons (fats), derived from both animal and vege- 

 table food. 



Carbohydrates, derived chiefly from vegetable foods. 



Water. 



Oxygen, taken from the air by the respiratory organs into 

 the blood. 



Salts, of various kinds in the foods. 



The outgo of an animal consists of: 

 Carbon dioxid, excreted from the respiratory organs. 

 Water, excreted from the skin, kidneys, and some other 

 organs. 



Urea, excreted by the kidneys or their equivalents. 

 Proteids, eliminated in the reproductive bodies. 

 Salts, in various excretions. 



After an animal has reached its full growth, the income and 

 the outgo practically balance. With some animals this period 

 of equilibrium lasts a long time, perhaps for years. With 

 others, growth may continue until death comes, in which ^ase 

 there is never any period of actual balance. 



The income of a plant consists of: 

 Carbon dioxid, from the air. 

 Water, from the soil. 

 Minerals, from the soil. 



The outgo of a plant consists of: 

 Oxygen, from the leaves. 

 Water, from the leaves. 



Carbon dioxid, from the leaves and other parts. 

 Proteids and various other substances, eliminated with dead 

 leaves, branches, seeds, and other reproductive bodies. 



No Sharp Distinction between Animals and Plants. The 

 criteria above given are ordinarily sufficient to distinguish 

 between animals and plants, and will separate typical forms; 



