CRITICISMS AND DIFFICULTIES 27 



affirm the necessary nature of an absolute determinism, based 

 on undisputed experiments. It could certainly not be affirmed 

 to-day. Yet the exact sciences have advanced since that 

 period, and one of the clearest benefits which we have gained 

 consists precisely in the new concept of determinism which 

 has profoundly modified the significance of our experimental 

 laws. To the physico-chemical law, which we had become 

 accustomed to consider as fatal and ineluctable, a statistical 

 law has been substituted, which, theoretically at least, admits 

 very rare exceptions, fluctuations according to the consecrated 

 term.^ The absolute determinism of the physical and chemi- 

 cal laws is now replaced by a statistical determinism which is 

 broader and more elastic, though practically as rigorous. 

 Curiously enough, Claude Bernard's act of faith, admittedly 

 based on an incomplete knowledge of phenomena, acquires 

 in the light of the progress of mathematical physics a character 

 of greater plausibility and generality. But contrary to what 

 the great physiologist might have thought, it is not by proving 

 the strictness qf the determinism which he brandished as the 

 emblem of his scientific philosophy, that the exact sciences 

 have given a more probable value to his words. On the 

 contrary, it is by opening the door to the possibility of very 

 rare fluctuations practically escaping calculation. To study 

 living organisms we are therefore obliged to depend on two 

 postulates. We need not define the first, for we momentarily 

 admit that it concerns the unknowable, the co-ordinated 

 effort, the plan. The second, and only one which counts for 

 us, estabUshes the identity of the laws governing inorganic 

 and organized matter. The latter alone has the value of an 

 indispensable working hypothesis. 



Our ideas have become more flexible since the works of 

 Gibbs and especially of Boltzmann. The 'determined' fact 

 has become a 'probable' fact. The law of great numbers is 

 at the base of all our physical laws. And now the old and 



^ For the development of these fundamental ideas, we again refer 

 the reader to Ch. E. Guye's book U Evolution physico'Chimiqiie (Chiron, 

 Paris, 1922), an admirably clear account of one of the most signifi- 

 cant and important advances of physico-chemistry. 



