128 EXPERIMENTAL EVOLUTION LECT. 



a daily witness to it. Professor Chauveau, from long, 

 and, as usual very careful experiments on Bacillus 

 anthracis, has been able to show that while no known 

 method can as yet, entirely destroy the pathogenetic 

 influence of this micro-organism, nor confer upon it 

 new and different properties, the pathogenetic influence 

 may be destroyed to the extent that it can no longer 

 harm the animals in which it makes itself the most 

 easily felt. Such virus may be inoculated into guinea- 

 pigs and mice without doing the slightest harm. But 

 it has not entirely lost its properties, since it retains 

 its vaccinal influence : while apparently no longer 

 noxious to animals, while producing no disease nor 

 pathological symptoms, it acts like a vaccine lymph, 

 and confers immunity against the inoculation of viru- 

 lent bacillus, as experiment shows. Again, these devi- 

 talised or altered bacilli, which only retain a vaccinal 

 influence, may be made to acquire virulence of the 

 highest type through very simple experimental pro- 

 cesses. Lastly, these attenuated bacilli retain their 

 new characters (of non-virulence and of mere vaccinal 

 aptitude) as long as is required, without it being 

 necessary to use particular methods of any sort, and, 

 as M. Chauveau remarks, if one were to consider 

 these bacilli in themselves, apart from their origin, 

 and without knowing what they may be made to 

 become under appropriate experiments, they might 



