GREAT STEPS IN EVOLUTION 73 



Characteristic Features of Living 

 Creatures. — The chemists tell us that the 

 physical basis of life always includes pro- 

 teids and similar highly complex substances, 

 and that the process of living involves an 

 intricate series of combustions and fermen- 

 tations and reconstructions, many of which 

 can be imitated outside the body altogether 

 and expressed in chemical formulae. On the 

 other hand we cannot give a chemical de- 

 scription of any complete vital function, or 

 of any activity of the living creature as a 

 whole — and unless, as the Germans say, we 

 throw away the baby with the bath, we can- 

 not ignore the most salient fact, that all the 

 manifold chemical processes are correlated 

 and controlled in a unified behaviour, in a 

 purposive agency. Even the amoeba is no 

 fool. 



The physicists tell us that the living crea- 

 ture resembles some wonderful kind of en- 

 gine; it is a material system adapted to 

 transform matter and energy; and it illus- 

 trates in its living a number of well-known 

 physical phenomena, of surface-tension, of 

 diffusion, of elasticity, of hydrostatics, of 

 thermodynamics, of electricity, and so on. 

 At the same time it has to be admitted that 

 not even the simplest vital activity, such as 

 the passage of digested food from the all- 



