63 



nique as was used to demonstrate the constancy of the types 

 of Pfeiffer's bacillus in animal passage and transference in man. 



Secondly it might be urged: It is admitted that all the types 

 of Pfeiffer's bacillus found cannot be the primary influenza 

 microbe; but a particular „pandemic type" might well be 

 discovered which really was the influenza bacillus. To this 

 it must be replied that from' the information available we must 

 assume that only a very few strains of Pfeiffer's bacillus cul- 

 tivated from influenza patients can belong to this type. But 

 then the principal reason for regarding Pfeiffer's bacillus as the 

 influenza microbe is lost, namely its widespread occurrence in 

 influenza. If it had not been possible to find this microbe 

 in more than a few per cent of influenza patients one would 

 certainly never have entertained the thought that it could be 

 the influenza bacillus. Just as little justification is there then 

 for the contention that a distinct race of Pfeiffer's bacillus, 

 which also at most could be demonstrated in a few per cent 

 of the patients, could be the primary influenza microbe and 

 that all the other Pfeiffer's bacilli with exactly the same general 

 biological characters were secondary organisms. 



Although therefore it must be said that our knowledge 

 of the occurrence and other relations of Pfeiffer's bacillus 

 strongly supports the idea that it is not the influenza bacillus 

 in its true sense, it must be admitted that there are still obscure 

 points which must be cleared up before we can confirm 1 this 

 with certainty. For instance we have not yet progressed far 

 enough to see clearly in what way the four following points 

 can be brought into harmony with one another. 



1. Pfeiffer's bacilli cultivated from influenza cases even in an epide- 

 mic which is well-defined as regards time and extent, consist as 

 a rule of a considerable number of different types. 



2. The type must in general be regarded as a constant character. 



3. In certain cases Pfeiffer's bacillus can be demonstrated al- 

 most constantly, immediately after the advent of influenza to the 

 locality. 



4. Apart from influenza epidemics Pfeiffer's bacillus can seldom 

 be found in healthy individuals. 



It must be pointed out that numbers 1, 2, and 4 can only 

 be regarded as probable. Our experience up to the present is 

 far from sufficient to prove their general validity. But let us assume 

 all four clauses are proved. What will be thought about the relation 

 of Pfeiffer's bacillus when through a single person influenza is 



