50 THE NATURE AND ORIGIN OF LIFE 



years ago l and it seems to me a handy expression for the law 

 of assimilation. 



Such a law of assimilation is rigorously exact in the very 

 special case of a bacterium cultivated with all the precautions 

 that prevent it from varying, but it is only approximate 

 in other cases. Still, as Helmholtz has done for the timbre 

 of sounds (see page 40), we can try to keep it scientifically 

 exact by discovering what phenomena are superadded to 

 the phenomenon represented by our equation ; for these 

 prevent it from corresponding with precision to what passes 

 in living nature. 



Destruction and Variation 



Our success is assured if we observe that, even in inorganic 

 chemistry, a definite compound is not limited to one way of 

 reacting in presence of a certain number of other compounds 

 equally definite ; the reactions which are produced in a mix- 

 ture of bodies depend on the conditions realized. There is 

 no reason beforehand why living substances should, from 

 this point of view, differ from ordinary not-living substances. 

 In our example of a bacterium which multiples without under- 

 going variation, we take precisely all the precautions neces- 

 sary to avoid the production of a single reaction other than 

 that which we wish to bring about. We realize experi- 

 mental conditions analogous to those of a body falling in 

 vacuo, and we obtain a formula as rigorously scientific as 

 the mechanical formula of the fall of bodies. 



But, on the other hand, we know that by treating a 

 bacterium by other bodies than its culture-medium by 

 sal-ammoniac or mercury bichloride, which are also chemical 

 substances we no longer obtain a multiplication, but a 



1 Theorie nouvelle de la Vie. Paris, Alcan, 3rd edition. 



