EVOLUTION AND MUTABILITY OF MATTER. 279 



coloration before reducing it ; the salt stops at the 

 stage which protects it best It stops at red, if it is 

 red light that assails it, because in becoming red by 

 reflection it best repels that light i.e., it absorbs it 

 the least 



It may then be advantageous, for the compre- 

 hension of natural phenomena, to regard the trans- 

 formation of inanimate matter as manifestations of a 

 kind of internal life. 



Conclusion. Relations of the Surrounding Medium 

 to the Living Being and the Brute Body. Brute 

 bodies, then, are not immutable any more than are 

 living bodies. Both depend on the medium that 

 surrounds them, and they depend upon it in the 

 same way. Life brings together, brings into conflict, 

 an appropriate organism and a suitable environment. 

 Auguste Comte and Claude Bernard have taught 

 us that vital phenomena result from the reciprocal 

 action of these two factors which are in close corre- 

 lation. It is also from the reciprocal action of the 

 environment and the brute body that inevitably 

 result the phenomena which that body presents. 

 The living body is sometimes more sensitive to 

 variations of the ambient medium than is the brute 

 body, but at other times the reverse is the case. 

 For example, there is no living organism as im- 

 pressionable to any kind of stimulus whatever as the 

 bolometer is to the slightest variations of temperature. 



There can only be, then, one chemically immutable 

 body namely, the atom of a simple body, since, by 

 its very definition, it remains unaltered and intangible 

 in combinations. This notion of an unalterable atom 

 has, however, itself been attacked by the doctrine of 

 the ionization of particles due to Sir J. J. Thomson; 



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