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. 
“‘T 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 
