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exclusively atypical Pfeiffers bacilli that were found in healthy 

 people, in fact in the majority of cases the greater number 

 of bacilli were typical. Thirdly, there is on the whole a 

 connection between the macroscopic appearance of the growth 

 and the microscopic picture, the macroscopically typical strains 

 most often showing on microscopic examination small regular 

 elements while the macroscopically atypical more frequently 

 consist of coarser elements of a more irregular shape. 



It will be further seen from the illustration that among 

 the typical as well as among the atypical strains there are 

 individual differences. Thus it will be observed that the up- 

 pennost strain (I 1) in contrast to the other typical one (I 5) 

 is inclined to spread itself on the surface by shooting out 

 tongue-shaped protuberances. In the case of the atypical strains 

 the meagre growth of the uppermost will be particularly noted. 



The difference between typical and atypical growth has 

 nothing to do with symbiosis as such, but usually it is displayed 

 most conspicuously in the symbiosis experiment, which is quite 

 intelligible as we have here in the same culture all possible 

 grades of growth from the weakest to the strongest. We thus 

 get a more complete picture of the growth of the individual 

 strain than could be done with ease by any other method. 

 But besides this, the difference between typical and atypical 

 growth will naturally assert itself on cultivation in pure cul- 

 ture on various media. On haemoglobin agar (or Fildes agar) 

 it is least noticeable as only specially atypical strains stand 

 out clearly from the typical. On blood agar the relation is 

 almost inverted, as we find here so good a nuance in the 

 appearance of the different strains that we venture to di- 

 stinguish between a large number of different types of growth. 



The most important of the characteristics of the atypical 

 growth, — both in the symbiosis experiment and on other 

 media where it obtains, — is the relatively dry and friable 

 constitution of the culture. The maximal intensity of the 

 growth is most often less than in the typical, but this is not 

 always so. Among the atypical forms are to be found all 

 degrees from the most intense symbiosis reaction to the very 

 weak, or even in a few cases, absolutely negative reaction. 



On the whole the strains which give a weak symbiosis 

 reaction, also grow comparatively poorly in pure culture on 



