178 ORIGIN AND NATURE OF LIFE 



into inorganic substances giving out on the 

 way its energy for the life processes of the 

 animal ; another part is built into reserve 

 chemical energy just as in the plant. There 

 are also whole classes of plants which derive 

 their energy just like animals, by living on the 

 chemical energy of other plants, or upon 

 animals. Such are the fungi and the bacteria 

 which produce disease when they invade the 

 bodies of plants or animals, or those which 

 act as purifiers by decomposing dead plant 

 or animal remains, reducing them to inorganic 

 constituents, and so completing the natural 

 cycle. In the process, energy is set free 

 and intermediately used by the bacteria 

 flourishing upon the dead matter. With the 

 exception of certain supplies of energy 

 utilized from winds and tides and waterfalls, 

 all the energy used by man for driving human 

 industries and concerns comes from past or 

 present sources of this kind, such as wood, 

 coal, petrol, and spirit which represent the 

 energy of the sunlight of past ages, either 

 immediate or remote. 



All the conveniences and luxuries of modern 

 civilization are dependent upon energy derived 

 from sunlight through the agency of the 

 transformer contained in the green plant cell. 



Now the green colouring matter, which acts 



