REPRESENTATIVE LAMARCKIANS 265 



every inoculation, the sieve 'mouse' whose meshes be- 

 come finer as the mouse grows older. Under such 

 conditions the bacilli multiply and undergo chance 

 variations in every direction. Among the bacilli 

 thus multiplied, however, those which have fortuitously 

 varied in the direction of decreased virulence are 

 caught in the meshes of the sieve 'mouse' which de- 

 stroys them, while those which have fortuitously varied 

 in the direction of increased virulence, pass through 

 the meshes and survive. The virulence increases with 

 each new generation of bacilli passing through mice, 

 that is, through the same sieve, which performs cease- 

 lessly the same selection." 



The same facts are now retold in the Lamarckian 

 vocabulary: "A sheep is inoculated with a bacillus. 

 This protean organism, like all living cells which con- 

 tinue to live, directs all its activity against the external 

 condition of its environment. When it finds itself in 

 the interior of a sheep it directs its struggle against 

 the sheep." 



In every living being a large number of activities 

 may take place and it is the sum total of prevailing 

 external conditions which foster the development of 

 some activities in preference to some others. Here it 

 is the activity of struggle or to use Le Dantec's ex- 

 pression, "the organ of struggle against sheep" which 

 will develop to greater extent, and consequently the 

 virulence of the bacilli will increase. They could 



