v] THE SOURCES OF FOOD 121 



live, until in the end there would only be one animal 

 left and it would die of starvation. The animals are 

 consumers, and their life-process may be regarded as 

 that of a clock which is always running down and 

 cannot be wound up except from the outside of 

 itself. 



The plants are producers for they can convert 

 inorganic into organic living substance. Carbonic 

 acid, salts of ammonia, and nitric acid exist in 

 nature and can come into existence apart from the 

 agency of life, and these very simple substances can 

 be synthesised to form proteid and carbohydrate. All 

 living substance therefore arises from the carbonic 

 acid of the atmosphere or the sea-water, and from 

 simple mineral nitrogen compounds, mainly by means 

 of the agency of plants. The pastures of the land 

 are the main sources of terrestrial animal life, and the 

 diatoms, peridinians and other vegetable planktonic 

 organisms are the pastures of the sea. 



All animal life is destructive and its continuance 

 implies the degradation of chemical compounds. 

 Proteid, carbohydrate and fat are compounds pos- 

 sessing high potential energy, that is they can be 

 oxidised or burned, as coal is burned, giving a large 

 amount of heat or energy ; or they can be decomposed, 

 as an explosive is decomposed, also yielding heat and 

 energy. When taken into the tissues they are 

 oxidised or decomposed and energy is obtained, and 



