2 BIOLOGY. [Boos i. 



more. Without stopping, as a few years ago M. Littre did, to 

 discuss the point whether the certitude of the existence of the 

 external world is of first or second quality, leaving aside every 

 metaphysical refinement, we must first firmly believe in the real 

 existence of the external world ; because all our senses cease not 

 to cry to us in every tone that the objective, the Non-He of the psy- 

 chologists, is not a chimera, because the contrary opinion would 

 strike with nullity all observation, all experience, all reasoning, 

 all knowledge. 



The reality of the exterior world once admitted, and man 

 never having been led to doubt that reality, except through a 

 species of intellectual depravation, people naturally inquired 

 what could be the internal constitution of the substance of the 

 universe. They suspected that behind the appearance infinitely 

 mobile and varied of the exterior phenomena there might exist 

 a general and related force. Our object in this work not being 

 to pass in review the opinions or the reveries of the different 

 philosophical schools, we make haste to expound the most pro- 

 bable theories and systems, those which observation has confirmed, 

 and which by slow degrees have conquered in science their right 

 of citizenship. 



Leucippus seems to have been the first to have had the intuition 

 of the most rational theory on the constitution of the universal 

 substance. In his opinion this substance is a discontinuous mass 

 of granules, solid, infinitely small, separated by void spaces. It 

 is " the void mingled with solid," according to an expression of 

 Bacon. 



Democritus admitted that these primordial granules were full, 

 impenetrable, moreover insecable, and, for this last reason, he 

 called them atoms? But the conception of atoms, full and dis- 



1 For what is it that Democritus says? "That there are substances in 

 infinite number, which are called atoms, because they cannot be divided, which 

 are, however, different, which have no quality whatever, are impassible, which 

 are dispersed here and there in the infinite void, which approach each other, 

 gather themselves together, enter into conjunction ; that from these assem- 

 blages one result appears as water, another as fire, another as tree, another 



