254 ZOOLOGICAL PHILOSOPHY 



substances of living bodies, is due to the sole condition capable of 

 giving it existence. 



In order to be understood, I should mention that two hypotheses 

 have been tried with a view of explaining all the facts bearing on 

 existing compounds and their transformations, and on the ele- 

 mentary combinations that we can ourselves form, break up and 

 then re-establish. 



The one generally received is the hypothesis of affinities : it is 

 well known. 



The other, which is my own special theory, rests on the assumption 

 that no simple substance whatever can have a tendency of its own 

 to combine with any other, that the affinities between certain substances 

 should not be regarded as forces but as harmonies which allow of the 

 combination of these substances, and lastly, that they can never 

 combine except when constrained by a force external to themselves, 

 and then only when their affinities or harmonies permit of it. 



According to the received hypothesis of affinities, to which chemists 

 attribute active special forces, the whole environment of living bodies 

 tends to their destruction ; so that unless these bodies possessed within 

 them a principle of reaction, they would soon succumb to the action of 

 surrounding substances. For this reason men have been unwilling 

 to admit the fact that there exists an exciting force of movements 

 in the environment of every body, living or inanimate ; and that among 

 the former it succeeds in setting up the phenomena which they present, 

 whereas among the latter it brings about a series of changes permitted 

 by the affinities and finally destroys all existing combinations. The 

 supposition is preferred that life only maintains and develops that series 

 of phenomena found in living bodies, because these bodies were sub- 

 jected to laws that were altogether peculiar to them. 



It will no doubt be recognised some day that affinities are not forces, 

 but that they are harmonies or kinds of relationships between certain 

 substances, which enable them to enter into a more or less close com- 

 bination through the agency of a general force outside themselves 

 which constrains them to it. Now since the affinities vary between 

 different substances, those substances which displace others from 

 their combinations only do so because they have a greater affinity 

 with certain of the principles in those combinations ; they are 

 assisted in this act by that general exciting force of movements 

 and by that which works for the approximation and union of all 

 bodies. 



As to life, all that ensues from it during its residence in a body results, 

 on the one hand, from a tendency of the constituent elements of com- 

 pounds to free themselves from their state of combination, especially 



