HISTORICAL. 17 



exception in favor of the cilia, of which the ex- 

 istence has been recently verified in the case of 

 several of the bacteria by divers botanists, among 

 others by MM. Cohn and Eug. Warming. 



Dujardin (1841), in his " Histoire Naturelle des 

 Zoophytes," preserved the family of the vibrioni- 

 ens of Ehrenberg among the infusoria, characteriz- 

 ing them as follows : " fiiliform animals, extremely 

 slender, without appreciable organization, without 

 visible locomotive organs." He made but few 

 modifications, of which the principal consisted in 

 uniting Spirochcela with Spirillum, Dujardin. Re- 

 jecting the character that Ehrenberg drew from 

 the rigidity of the spirilla, the Spiroehceta plica- 

 tilis, Ehrb. became the Spirillum plicatile, Duj. ; 

 but, as will be seen later, this change has not 

 been maintained. Dujardin, then, classed the bac- 

 teria in : 



1. Bacterium : filaments rigid, with a vacillating 

 movement. 



2. Vibrio : filaments flexible, with an undulatory 

 movement. 



3. Spirillum : filaments spiral, movement rotary. 



Until this time the bacteria had been considered 

 as animals placed at the foot of the series. Sub- 

 sequently the tendency to place them in the 

 vegetable kingdom became more and more pro- 

 nounced. 



Already, since 1853, M. Ch. Robin had pointed 

 out the relationship of the bacteria and of the 



2 



