118 CLASSIFICATION OF FISSION-FUNGI. 



fortunately, we hold the fulfilment of this hope most im- 

 probable, and look for the simplification of our subject 

 through approaching the question from a different point 

 of view and by an improved nomenclature. 



In every species of bacterium which is closely studied, 

 there are found closely related forms that not rarely rep- 

 resent to the unprejudiced unbroken links to other species. 

 I will recall only the discoveries which have been made 

 regarding the streptococci, the colon group, the diphtheria 

 organisms, and the relatives of the cause of tuberculosis, 

 which so long stood almost entirely isolated. 



With this condition of things I have sought to apply to 

 bacteria, with the greatest possible care, the principles 

 which have been found satisfactory with the pleomorphic 

 phanerogams, with which I have worked for years. With 

 the principal varieties, which were completely described, 

 we have grouped related varieties without assigning to the 

 latter the rank of varieties. We omit this, because we 

 must have made changes in the nomenclature, but espe- 

 cially because also the principal varieties are often separated 

 from each other by characteristics that would scarcely be con- 

 sidered as sufficient for the characterization of varieties in the 

 botany of higher plants. It is naturally almost impossible 

 to state exactlj' the grade of relationship between closely 

 standing varieties, and it often becomes a matter of taste 

 whether one states ' ' identical with the preceding variety ' ' 

 or ' ' very closely related, ' ' etc. We certainly believe it 

 belongs to the future to convert varieties of bacteria into 

 others, in a manner scarcely to be imagined to-day. The 

 forms of the Micrococcus pyogenes are convertible into 

 each other; the Bacterium pyocyaneum and Bacterium 

 fluorescens can, indeed, almost certainly be converted into 

 each other; and similar statements regarding typhus and 

 coli, diphtheria and pseudodiphtheria, etc., are always 

 still looked upon with skepticism, but the possibility, yes 

 even the probability, can scarcel)' be contested any more. 



In spite of all the things wliich make a rational division 

 and classification of bacteria more than ever difficult, we 

 take the stand that it is absolutely essential to strive after 

 it, and that also for medical men the division of bacteria 

 into pathogenic and non-pathogenic, etc. , as is still always 



