12 ORGANISMS AND ENERGY. 



animals, mean an enormous and ceaseless expenditure of 

 energy, and the question naturally arises, Whence is this 

 energy obtained? 



We find that the chemical decomposition of the 

 constituents of protoplasm, such as proteids, results in a 

 sttting free of chemical energy. We have seen that pro- 

 teids and less complex carbohydrates are brought directly 

 into the body of the animal as food, so we are forced to 

 look beyond the animal itself for the source of energy. 



On the other hand, these complex carbon compounds 

 are built up or manufactured by the plant from simple 

 constituents within it. In this building-up the same 

 amount of energy has to be supplied as is again set free 

 in movement and heat in the subsequent decomposition. 

 This building-up, or the chief part of' it, is effected in the 

 plant by a process not fully understood, but certainly 

 requiring a supply of radiant energy from the sun's rays. 



Hence we are led to two important conclusions : — 



1. The animal kingdom is entirely dependent (or parasitic) upon 



the vegetable kingdom for all its energy. 



2. The vegetable kingdom accumulates vast stores of energy in the 



formation of complex chemical compounds, derived from the 

 radiant energy of the. sun. 



Organisms may be regarded as complex machines for 

 transmutation of energy. The work of plants is the 

 transmutation of kinetic (radiant) into chemical energy, 

 and that of animals is (like that of steam-engines) the 

 transmutation of chemical into kinetic energy. 



We must therefore look to the sun as the sole source of 

 every movement, thought or impulse of the animal creation. 

 Plants and animals have the same essential living matter or 

 protoplasm, but with certain marked differences in form and 

 function. These are more pronounced in the higher types, 

 but when the simplest living organisms are studied the 

 distinctions break down. Supposing the two kingdoms are 

 of common descent this state of affairs is to be expected. 



We have thus passed in review the various physical, 

 chemical and vital properties of living matter, as found in 

 the organic world, and have noticed the main underlying 

 distinctions between the vital functions of plants and 

 animals. 



