1.8 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



phase. (2) Compounds of high potential — carbohydrate, 

 fat and proteid are broken down, re-synthesised, and 

 again broken down into compounds of low potential — 

 carbon dioxide, water, and (ultimately) nitrate, and work 

 is done by the organism in the form of movements 

 controlled by its sensory-motor system. This is the 

 animal phase. 



That is to say, the organism, considered as a 

 physico-chemical mechanism, may be compared with the 

 imaginary mechanism known to physics as a reversible 

 Carnot heat-engine. But the natural processes known to 

 physics belong only to the positive half of the Carnot 

 cycle : in them energy falls from a state of high to a 

 state of low potential as in the metabolism of the animal. 

 The reverse process, corresponding to the metabolism of 

 the plant, in which energy passes from a state of low to 

 a state of high potential is only conceived by physics, or 

 can only be approximated to by operations directed 

 by human intelligence. Further, the transformations 

 studied by physics occur necessarily under conditions 

 which lead to enormous waste, that is, the energy which 

 should appear as work done * becomes dissipated as 

 unavailable heat at uniform low temperature ; whereas 

 the transformations studied in the metabolism of the 

 organism proceed with so little loss of available energy 

 that one may say that this waste tends to vanish. There- 

 fore, the second law of thermodynamics does not 

 necessarily apply to the organic mechanism while 

 necessarily applying to the inorganic one. 



I have assumed that in the metabolism of the 

 organism the energy necessary for the construction of 

 carbohydrate from water and carbon dioxide is absorbed 

 from radiation. Now while this is the case with the 

 green plant it is not apparently the case with the 



