CLASSIFICATION OF THE BACTERIA. 63 



vinced," he says, " that the schizomycetes cannot 

 be grouped in accordance with their action as fer- 

 ments and their exterior forms, and that altogether 

 too many species have been distinguished ; so, on 

 the other hand, it seems to me very improbable 

 that all the schizomycetes constitute a single natu- 

 ral species. 



" I am rather inclined to suppose that there exists 

 among them a small number of species, which 

 have little in common with the genera and species 

 admitted to-day, and of which each runs through a 

 cycle of determined forms sufficiently numerous. 

 Each of the veritable species of schizomycetes is 

 not limited to presenting itself under the different 

 forms of Micrococcus, Bacterium, Vibrio, and Spi- 

 rillum, but can also show itself as the agent of 

 acidification of milk, of putrefaction, and as the 

 agent producing several maladies." However, 

 Nageli recognizes that it is necessary to distin- 

 guish these forms, notably those of Micrococcus, 

 Vibrio, Bacterium, and Spirillum, without, how- 

 ever, losing from view the fact that the organisms 

 thus classified have a very inconstant constitution, 

 and pass continually from one form to another. 



Finally, other savants such as M. Pasteur, take 

 less account of the structural characters than of 

 the physiological functions, regarding as a partic- 

 ular species every form of bacterium .which is born 

 constantly in a determined medium, or which 

 causes a special kind of fermentation. 



Nageli opposes to this view the following 

 objections. First, he has verified the presence, in 



