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atypical strains has already been sufficiently established, we 

 will confine ourselves to comparing the typical strains from 

 different sources. It will be easily perceived that no con- 

 nection among the typical strains can be demonstrated between 

 the habitat on the one hand, and the dependence upon hae>- 

 moglobin, the macroscopic and microscopic morphology of the 

 culture, the minimum 1 temperature for growth, the resistance 

 against heating, and indol production etc. on the other hand. 

 A similar statement could be prepared with regard to agglu- 

 tination, as has been done in the case of the indol reaction. 

 This however would hardly be worth while. It will be obser- 

 ved that agglutination between the different groups (influenza, 

 whooping-cough, meningitis, and healthy persons) is practi- 

 cally just as common as between strains and sera belonging 

 the the same group. The only difference is that positive reac- 

 tions among the strains from healthy persons do not occur 

 quite as frequently as among strains from influenza etc. This 

 is easily explained on the assumption that besides the atypical 

 forms others may be met with in healthy persons which 

 do not usually occur in influenza. 



(I did not succeed in making suspensions of the guinea-pig 

 strains which could be used for agglutination. Otherwise no im- 

 portant difference could be found between these and the atypical 

 strains from man). 



It would naturally be interesting to find out whether the 

 „mutations" observed in several strains and incidently already 

 referred to, are genuine, or are due to contamination; but as 

 previously said this would involve a very difficult piece of 

 work from a technical point of view which the main portion of 

 the investigation did not leave time for. 



The most important phenomena will however be briefly 

 mentioned. 



Among the strains, numbering about 60, of which plate cul- 

 tures were made with a view to investigating the form of colony, 

 it was usually observed that all the colonies of a single strain 

 which were so remote that they were not appreciably influenced 

 by their neighbours, were practically of the same appearance. In 

 cases however, two distinctly different types of colony were ob- 

 served on the same plate, (a lighter and a darker, with or without 



