197 



it is less marked, to those in which, at all events in a single 

 test, it may be entirely absent. Furthermore the same strain 

 when repeatedly examined may at one time exhibit no symbio- 

 sis" and at another exhibit it to a more or less marked degree. 

 In the majority of cases where the symbiosis reaction is present 

 it must however be reckoned as a special characteristic of 

 Pfeiffers bacillus, as will be clear from a comparison with 

 Bordet's bacillus and Bacillus haemoglobinophilus canis. 



All the morphological and „cultural" charac- 

 ters, as they are described in the chapters on symbiosis, growth 

 on blood agar, form of colony, and microscopic morphology, 

 together constitute a rather wide, but not unlimited, „series" 

 within which all possible transitions are to be found. Never- 

 theless a rough but useful division into „typical" and „aty- 

 pical" strains can be made (see the scheme on p. 145). 



Absence of spore formation is a constant charac- 

 ter; this applies, for all practical purposes, to the absence 

 of motility. All the strains examined were distinctly 

 aerobic, by the method of investigation employed. 



As regards the reaction of the medium, they behave 

 practically the same as most other bacteria which are cultivated 

 from man. Differences within the group could not be demon- 

 strated. 



The investigation of the minim u mi temperature for 

 growth shows three things: (1) the group as a whole, has 

 rather restricted boundaries as regards this factor; (2) each 

 strain, at any rate to some extent, has its own temperature mi- 

 nimum; (3) there appear to be gradual transitions with regard 

 to the situation of the temperature minimum. 



The resistance against heating was always slight; 

 but is should be pointed out that while the death-point, under 

 the experimental conditions, for most of the strains can be 

 taken to lie between 46° and 50°, a few strains were more re- 

 sistant, and the fact that all were distinctly atypical is greatly 

 in favour of the fact it is more than a chance experimental 

 irregularity. 



Slight resistance to drying and keeping of sur- 

 face cultures which are subcultured must be regarded as a 

 characteristic of the whole group. Doubtless there are in- 

 dividual differences between the strains in this respect also, 



