CHAPTER III A 



METABOLISM. 



i. IN the early forties the French chemist Dumas 

 pointed out the opposed actions of the vegetal and animal 

 kingdoms: the one having for its chief chemical effect the 

 decomposition of carbon-dioxide, with accompanying assimila- 

 tion of its carbon and liberation of its oxygen, and the other 

 having for its chief chemical effect the oxidation of carbon and 

 production of carbon-dioxide. Omitting those plants which 

 contain no chlorophyll, all others de-oxidize carbon ; while all 

 animals, save the few which contain chlorophyll, re-oxidize 

 carbon. This is not, indeed, a complete account of the general 

 relation; since it represents animals as wholly dependent on 

 plants, either directly or indirectly through other animals, 

 while plants are represented as wholly independent of ani- 

 mals; and this last representation though mainly true, since 

 plants can obtain direct from the inorganic world certain 

 other constituents they need, is in some measure not true, 

 since many with greater facility obtain these materials from 

 the decaying bodies of animals or from their excreta. But 

 after noting this qualification the broad antithesis remains as 

 alleged. 



How are these transformations brought about? The car- 

 bon contained in carbon-dioxide does not at a bound become 

 incorporated in the plant, nor does the substance appropriated 

 by the animal from the plant become at a bound carbon- 

 dioxide. It is through two complex sets of changes that 



