196 



being cultivated from man and a few from guinea-pigs. We 

 will now enquire whether there are any grounds for believing 

 that all these strains together constitute a natural group and 

 whether this can be further divided into sub-groups. By a 

 natural group is merely understood one which is formed by a 

 rational classification, as explained on p. 98. 



The questions which the previous part of this investiga- 

 tion should have made it possible to answer are the following: 

 (1) Have all the strains examined so much in common 

 that it as justifiable to place them in one group? In connection 

 with this it must also be enquired to what extent the charac- 

 ters examined permit of a sufficiently sharp limitation 

 of the group. (2) Are there gradual transitions in the 

 group, or does it naturally fall into sub-groups? In order that 

 the last question may be answered absolutely in the affirmative 

 it is requisite that a decided jump between the different 

 grades of several of the characters, be demonstrated, and that 

 a constant connection between the various characters be present. 

 With these different questions in mind we will briefly 

 review the characters that have been investigated. 



That all the bacteria grow rapidly, and are markedly 

 h a e m o g 1 o b i n o p h i 1 i c, n o n - h a e m o 1 y t i c, Gram ne- 

 gative rods, follows from the definition on pp. 99—100, where 

 the results of the following investigation are also foreshadowed 

 in so far as it was remarked that haemoglobinophilia, absence 

 of haemolytic power, decoloration by Gram's method and the 

 rod-shape are each of them characters which allow of a sharp 

 distinction from bacteria which behave in a different manner. 

 As regards haemoglobinophilia the original definition must 

 however be modified as follows: Complete absence of the power 

 of growing on ordinary agar; the same is usually also the 

 case on, as far as possible, blood-free ascitic agar, on which 

 medium however a slight growth is not excluded. But it is 

 required that in all cases the growth on such „haemoglobin" 

 media, which on the whole have proved particularly suitable 

 to Pfeiffer's bacillus, shall be far richer than on ascitic agar. 

 The symbiosis phenomenon has proved not to be 

 an obligatory character of Pfeiffer's bacillus; this is excluded 

 by the gradual transitions from strains which constantly give 

 this reaction to a marked degree, through strains in which 



