64 



introduced into a hitherto influenza-free neighbourhood and in the 

 course of a short time spreads throughout it, and then this .mi- 

 crobe is found from the first in large quantities in all the influenza 

 patients'?' On the assumption of the absolute validity of the four 

 statements it cannot have been introduced with influenza because 

 then it ought to be . the same type in all the patients. We are 

 almost compelled to assume it was present in all the individuals 

 concerned before the influenza arrived but either in such small 

 numbers that it could only rarely be demonstrated, or in such 

 an attenuated condition that it could not be cultivated. If we give 

 up the idea of the absolute validity of one or more of items 1, 2, 

 and 4, there are of course, other explanations possible. For example 

 we might suppose that in those cases where Pfeiffer's bacillus is 

 found in all the patients immediately after the arrival of influenza 

 in a locality, either we should have been able by a thorough 

 examination to obtain it in all healthy persons before the epidemic, 

 or by comparing the strains of Pfeiffer's bacilli from patients in- 

 fected with influenza from the same source we should find I hey 

 were serologically identical. 



These considerations are sufficient to show that there are 

 still many aspects that need further explanation before we 

 can establish the negative with the greatest certainty, namely 

 that Pfeiffer's bacillus is not the true influenza bacillus. 



There is so much however to support this view that the 

 great majority of bacteriologists have more or less decisively 

 rejected the classical conception of the role of Pfeiffer's ba- 

 cillus as the microbe of influenza. But even for him who 

 completely abandons the conception of Pfeiffeh, the ba- 

 cillus, — in virtue of its wide distribution, its pathogenic 

 qualities, and its characteristic nutritional requirements, — will 

 be a worthy object for continued bacteriological research 



