78 Synopsis of the Bacteria and Yeast Fungi. 



the so-called species, in various media and under varying 

 circumstances, with the aid of all the modern refinements 

 for keeping the cultivations pure. 



There is still another speculation to which the facts 

 appear to lead the way. A species such as those investi- 

 gated by Zopf is called a " Protean " species, and the 

 various forms are considered to be a series of adaptations 

 to the environment. Nageli, as we have seen, carried the 

 theory so far as to assert that there are no real species 

 among the Schizomycetes ; and Buchner considered that 

 he had transformed the harmless Bacillus subtilis by cultiva- 

 tion into the virulent B. anthrads, although his conclusions 

 are controverted by Cohn, Klein, and others. Much of the 

 disputation on this topic of " species " arises from the fact 

 that many persons cannot readily conceive a species in the 

 new light which the Darwinian theory has thrown upon it. 

 There can be no doubt that new species not only may, but 

 actually must, be making at the present moment. It is not 

 generally recognised that, to our floriculturists, the making 

 of what would, if spontaneous, be universally considered a 

 new species has been a frequent occurrence. Not only is 

 it probable that B. anthrads was developed from B. subtilis 

 (whether Buchner's conclusions be true or false), but man, 

 by a change of environment if continued long enough, 

 may at any time produce a similar change in another species. 

 During the siege of Paris, small-pox continued its ravages, 

 gradually assuming a more virulent and malignant form ; 

 the cause of this can only be that the micro-organism of 

 small-pox was changing its physiological nature, and, had 

 the conditions been constant for a sufficient length of time, 

 it might ultimately have formed what would be to all 

 intents and purposes a new species. Pasteur's "cultiva- 

 tion" of disease-germs in order to reduce their virulence 



