24 Lectures on Bacteria. [$ iv. 



Examples of the other and simpler kind of arthrosporous forms 

 are to be found, according to our present knowledge, in the 

 forms described under the name of Micrococcus 

 (Fig. 4). Each vegetative cell may at any moment 

 begin to form a new series of vegetative cells ; there 

 is no distinction between specifically reproductive 

 F ' 1 S- 4- and vegetative cells. 



The entire distinction between endosporous and arthro- 

 sporous Bacteria is required by the present state of our know- 

 ledge. It remains to be seen whether and to what extent it will 

 be maintained. Our knowledge is at present still so incomplete 

 that we must on the one hand regard the discovery of endo- 

 genous formation of spores as possible or probable in forms 

 where they are hitherto unknown, even in the simplest Micro- 

 cocci, and I say this to prevent all misunderstanding; and on 

 the other hand we cannot say that facts will not come to light 

 in course of time which will do away with any sharp separation 

 between the two divisions. 



IV. 



Species of Bacteria. Distinct species denied. The 

 grounds for this denial insufficient. Method of in- 

 vestigation. Relationships of the Bacteria and their 

 position in the system. 



HAVING now made ourselves acquainted with the course of 

 development in Bacteria in its main features, we proceed to 

 consider the much-debated question whether there are specifi- 

 cally distinct forms, species of Bacteria, as these terms 

 are used in descriptive natural history, and how many such 

 species can be determined. Species are determined by the 

 course of development. By the term species we mean the sum 



Fig. 4. Micrococcus Ureae, Cohn, from putrifying urine. Single cells 

 and cells united in rows (= Streptococcus). Magn. noo times. 



