The individual colony. 



Growth on blood agar. 



Growth in symbiosis test. 



145 



Typical. 

 Rather large, semitrans- 

 parent with well develo- 

 ped granulations, but 

 otherwise homogene- 

 ous. 



Quite small, flat clear 

 colonies which form a 

 confluent culture . of a 

 fairly homogeneous sur- 

 face. 



Vigorous symbiosis ; the 

 heavy growth is pure 

 white by reflected light; 

 it is confluent, and of 

 soft homogeneous con- 

 sistence. 



Atypical. 

 Small, more opaque. 

 Granulations absent or 

 weakly developed. Cul- 

 ture often slightly he- 

 terogeneous. 



Colonies more arched 

 and grow more isola- 

 ted from one another. 



All degrees from ab- 

 sent to marked sym- 

 biosis are found. Growth 

 more greyish or yello- 

 wish, dry and friable. 



Occurrence. 



Influenza, whooping- Frequent in healthy 

 cough, measles, menin- persons and in measles, 

 gitis, healthy persons. rarer in influenza and 

 whooping-cough. 



The great differences in macroscopic morphology between 

 different strains of Pfeiffer's bacillus is undoubtedly not yet 

 generally appreciated. Rivers (1) and Skajaa's experience 

 however, agrees well with that reported here. 



Microscopic Morphology. 



If, in investigations into the occurrence of Pfeiffer's bacillus, 

 we accept the description of its morphology given in one 

 of the ordinary bacteriological textbooks, we shall undoubtedly 

 be liable either arbitrarily to adopt a too stringent limitation 

 of the findings counted as positive, or fall into a dilemma with 

 regard to the extent to which we shall admit forms that diverge 

 from the picture described as typical. There is every reason 

 to believe that numerous workers have obtained too few po- 

 sitive results from this cause, particularly in examinations of 

 healthy people. 



In my investigations it has come to light that among bac- 

 teria which I gradually realised must be included in the 



10 



