METABOLISM 57 



we study the non-living. We endeavor 

 to discover its underlying mechanism 

 and to bring it under our control. 



When we compare the organism to a 

 candle flame, we are struck by certain re- 

 semblances. Both are in dynamic equi- 

 librium, that is, they retain their form 

 while continually changing their sub- 

 stance; both carry on processes of com- 

 bustion which may start with the same 

 substances and end with the same prod- 

 ucts, and set free the same amounts of 

 energy; both respond to changes in the 

 environment, such as variations in the 

 supply of oxygen or in temperature. 



We might go on to point out other re- 

 semblances but it will perhaps be more 

 instructive to consider the points of dif- 

 ference. In the first place the combus- 

 tion of the organism proceeds at a rela- 

 tively low temperature. This depends 

 upon the fact that it takes place in wa- 

 tery solution : such combustion can easily 

 be imitated in the laboratory. It is 

 greatly facilitated by certain enzymes. 



