71 



The technique described above was in the main developed 

 in the course of the first 2 months' work with Pfeiffer's ba- 

 cillus. The choice of the method of investigation was na- 

 turally made on the basis of the statements in the literature 

 about the characteristic qualities of this microbe. 



With regard to comparison with the investigations of others 

 it must be pointed out that most of the authors who have 

 reported investigations on Pfeiffer's bacillus in a large number 

 of persons have restricted themselves to observing the appea- 

 rance of the colonies in the original culture, making a microsco- 

 pic examination and demonstrating the absence of growth on 

 haemoglobin-free media. 



As one of the objects of my research has been to investi- 

 gate how Pfeiffer's bacillus may be mbst rationally separated 

 from other kinds of bacteria, it was naturally not a foregone 

 conclusion that this technique and the boundaries fixed by 

 it would bear the criticism of the subsequent more thorough 

 investigations. This point will be further discussed later on. 

 It need only be mentioned here that in the light of my later 

 experiences hardly any errors have been committed in the 

 investigation of influenza cases, but that in the inocula- 

 tion from healthy persons decisions have probably been 

 arrived at in isolated cases, which in view of later experience 

 must be judged as inaccurate, without it having been possible 

 afterwards to rectify the error. It may be that a few haemb- 

 lytic, haemoglobinophilic bacteria have been called Pfeiffer's 

 bacilli; and again one or two of the first series of investiga- 

 tions of healthy persons presumably might have given a rather 

 larger number of positive findings of Pfeiffer's bacilli if they 

 had been performed with the aid of the technical experience 

 I have since gained. 



On the whole it must be contended however that uncertainty 

 in the correct limitation of Pfeiffer's bacillus has only played 

 a very subordinate role. 



The investigations into the occurrence of Pfeiffer's bacillus 

 can naturally be divided up according to the conditions under 

 which they were carried out, and fall therefore into the fol- 

 lowing groups: 



