PROSPECTS FOR A NATURAL SYSTEM OF CLASSIFICATION OF BACTERIA 



dingungen, unter denen sie uberhaupt zu leben vermogen, wiirde sich 

 all ihre Formen und Eigenschaften in Abhangigkeit von diesen Bedin- 

 gungen merken und sie in die Diagnose der betreffenden Linie auf- 

 nehmen. Alle die reinen Linien, die dann keine Unterschiede in der 

 Diagnose aufweisen wiirden, miisste er zu systematischen Einheiten 

 zusammenfassen, zu sog. elementaren Arten, und diese von willkiir- 

 licher Umgrenzung wenigstens einigermassen freien Einheiten nach 

 Gutdunken zu hoheren Einheiten zusammenfassen. Tatsachlich ist 

 das nicht moglich; das braucht nicht weiter begriindet zu werden, 

 denn jene eben skizzierte Arbeit wiirde kein Ende absehen lassen. So 

 miissen denn fur die praktischen Zwecke der Systematik, d.h. um eine 

 Ubersicht liber die Formen zu ermoglichen, hohere systemaiische Ein- 

 heiten gewahlt werden.' 



Hence it follows that in an attempt to subdivide the organisms be- 

 longing to one 'natural' group of bacteria into species one shall have to 

 create as many species as there are organisms which differ in 'suf- 

 ficiently fundamental' characters, regardless of the possible existence 

 of intermediate types. It depends entirely upon the 'scientific tact' of 

 the investigator which characters will be deemed worthy of the desig- 

 nation 'sufficiently fundamental'.* 



It is here the place to give a short survey of the characters which may 

 be taken into consideration in this respect. 



a. Morphological characters 



It is self-evident that the shape of the cells is of outstanding importance 

 for determining the place of a bacterium in any phylogenetic system. 

 The same holds, of course, for the mode of reproduction and the oc- 

 currence of special resistent stages such as endospores, gonidia etc. In 

 addition to these characters the size and the structure of the cells may 

 give valuable indications. 



With regard to structure it is especially the presence of organs for 

 locomotion, flagella, and the way in which they are attached to the 

 cell which has long been recognized as affording insight in mutual 

 relationships. In this connexion it must, however, be remarked that 

 experience has taught that in cases of immotility of the cells we have to 

 discriminate beiween 'incidental' and 'genuine' immotility. For, as has 



* It goes without saying that similar difficulties will also be encountered in marking 

 off the higher systematic units, though to a lesser extent. 



287 



