10 



At that time there was very scanty information in the litera- 

 ture bearing upon the differences between the individual strains 

 of Pfeiffer's bacillus and upon possible connecting links between 

 this and other kinds of bacteria. The task of obtaining some 

 enlightenment concerning the classification of the haemoglo- 

 binophilic bacteria therefore immediately suggested itself. The 

 following points came up for consideration: 



1. How is Pfeiffer's bacillus to be distinguished from other 

 kinds of bacteria? 



2. Are well-characterised individual differences to be found 

 between the various strains and if so what are they? 



3. If the different strains of Pfeiffer's bacillus cannot be 

 regarded as identical among themselves, can they then be di- 

 vided into clearly defined groups or do all possible transitions 

 exist? ■ ' i : ■' ! I ' 



4. Can any relation be demonstrated between the location 

 of Pfeiffer's bacillus and its characters? For example are 

 Pfeiffer's bacilli from influenza distinct from those found in 

 healthy people or in whooping-cough? 



Such an investigation was required not only as a link 

 in the ordinary natural description of micro-organisms but, 

 as will be further explained in this work, it as also of con- 

 siderable importance as regards the question which has been 

 so much discussed since the beginning of the last pandemic, 

 namely the relation of Pfeiffer's bacillus to influenza. 



In order to elaborate a classification which should be as 

 natural, that is to say, unfortuitous as possible I have made 

 a point of examining a considerable number of cultures of 

 different origin and of investigating every culture in as many 

 different ways as possible. This work is therefore mainly of 

 a statistical nature. To make it practicable it was necessary 

 to employ very elementary methods of investigation. 



Concurrently with the carrying out of my investigations 

 a rather extensive literature covering the same ground has 

 appeared; and it appears that the various authors have largely 

 arranged their investigations on similar lines to those I had 

 in hand before I became acquainted with the works in que- 

 stion. On the whole my results agree with those recorded by 

 others. I have therefore not been able to bring forward much 

 which at the present moment can be regarded as new, but 



