48 



abnormal and the later cultures typical, and sometimes the 

 converse is the case. 



According to Wollstein (3) and others Pfeiffer's bacilli from 

 meningitis are usually bigger and longer than from the respira- 

 tory tract. This difference is however far from constant, and 

 in all it has not been possible to demonstrate any connection 

 between the habitat and the morphology (Davis (2)). 



On the whole there is general agreement that the mor- 

 phology of Pfeiffer's bacillus in every respect exhibits well- 

 graded intermediate forms so that any grouping on that basis 

 cannot be undertaken. 



Biochemical Reactions. 



We have now seen that the morphology is no more 

 suitable than the pathogenicity for animals, as a basis for 

 classification. As these factors, up to the beginning of the 

 last pandemic, were the only ones which had been examined 

 from this standpoint (apart from the first attempts at a serologi- 

 cal analysis), it cannot be wondered at that we were still not 

 in a position at that time to form an opinion as to how 

 far distinct differences between the individual strains of Pfeif- 

 fer's bacillus existed, or whether they were all to be regarded 

 as mutually identical. 



But during and after the pandemic numerous papers have 

 appeared dealing partly with the biochemical reactions of Pfeif- 

 fer's bacillus and partly with its serological reactions. 



Of ihe biochemical reactions i n do 1 'formation should 

 first be mentioned. That Pfeiffer's bacillus can form indol 

 was first proved by Rhein (1919). Subsequently Jordan (1), 

 Malonk (2;, Rivers (1,2), Rivers & Koiin, Povitzky & Denny, 

 and Yabe have all examined a number of strains of Pfeiffer's 

 bacillus for indol formation and they have all obtained the 

 surprising result that the strains fall into 2 fairly sharply 

 defined groups: some form indol easily while in others this 

 power is quite lacking. Intermediate forms, namely strains 

 possessing weak or doubtful indol formation seem only excep- 

 tionally to occur. The overwhelming majority of strains from in- 



