THE ORGANIC AND THE INORGANIC 339 



its energy from solar radiation because this is the most 

 abundant source of terrestrial energy. The human eye 

 is most susceptible to light of a particular frequency 

 of wave-length, but this is the radiation that is most 

 abundant in the light of the sun. Does this not mean 

 that the organism has merely adapted itself to the 

 material and energetic conditions in which it exists ? 

 Does it necessarily mean that because the conditions 

 were very different life could not exist ? Protoplasm 

 could not exist at a temperature of several thousand 

 degrees Centigrade, but does that mean that life, 

 which on any hypothesis of mechanism must be 

 described in terms of energy, could not exist in these 

 conditions ? 



It must have had an origin, says Weismann, 

 because it has an end. Organic things are destroyed, 

 inasmuch as they disintegrate into inorganic things. 

 Organisms die. Thus the organic process comes to an 

 end, and because it comes to an end it must have a 

 beginning. Spontaneous generation of life is thus, for 

 Weismann, a 'logical necessity." 



Need this logical necessity exist ? The argument 

 clearly implies that life is a reversible process. Organic 

 things become inorganic, and therefore inorganic things 

 must become organic things. The first statement is 

 a fact of our experience, but the second one would only 

 be logically true if we were to postulate that the process 

 of life, whatever it may be, is a reversible process. 

 But we must not postulate this if we are to hold to a 

 physico-chemical mechanism, for it is a fundamental 

 result of physical investigation that all inorganic pro- 

 cesses are irreversible : reversible inorganic processes 

 are only the limits to irreversible ones. Physical pro- 

 cesses go only in one way, and that organic substance is 

 destroyed to the extent that it becomes inorganic is a 



