PLEOMORPHISM OF THE SCHIZOPHYTA. 505 
taking the position of an artificial or formal system, whilst the 
natural species must be based upon some of those more pro- 
found characteristics which Cohn has himself indicated to us 
in his divisions—saprogenous, chromogenous, pathogenous. 
The indications of natural species do not lie under our hands 
in the case of the Bacteria, but have yet to be sought out.” 
I have now, I think, sufficiently pointed out the position of 
my publication on Bacterium rubescens in the history of 
the modern doctrine of the pleomorphism of the Bacteria. It 
will accordingly be readily understood that I cannot content- 
edly see this doctrine referred to, as it was recently by my 
friend Dr. Klein, as “‘ Nageli’s theory of the pleomorphism of 
the Schizophyta,” since Nageli’s view was announced four 
years after my publication, and is not identical with that at 
present accepted by De Bary, Zopf, and others, which is, in 
fact, precisely that put forward by me in 1873. Some of 
the recently published books dealing with the cultivation of 
pathogenic Bacteria contain also a general summary of what 
is known as to the natural history of the group, and an attempt 
to classify the non-pathogenic together with the pathogenic 
species. The importance of the doctrine of the pleomorphism 
of Bacteria in relation to pathological inquiries cannot be over- 
estimated. It is therefore to be desired that in future editions 
the authors of the books referred to above will give a correct 
account both of the history and present position of this 
doctrine. 
