18 



gations at any rate have not supported him. He does not 

 appear to have examined healthy subjects. Later he announ- 

 ced (2) that in addition to typical influenza cases it was also 

 found in „ambulatory influenza" where the most important 

 symptoms were a cold and fever, and in „chronic influenza" 

 which usually developed in a phthisical case. (Half a year 

 after the epidemic had ceased Pfeiffer's bacilli could no longer 

 be demonstrated in phthisical cases). The reason he regarded 

 these cases as influenza depended partly on the fact that 

 they had more severe general symptoms than an ordinary 

 cold or phthisis, and in the case of phthisis because the spu- 

 tum had a different appearance to what we are accustomed 

 to see in lung tuberculosis, and also partly on account of the 

 finding of „influenza-bacilli". But in accordance with our pre- 

 sent view we may doubt the justification of calling such cases 

 influenza. We are immediately up against the great difficulty 

 that the disease does not display such characteristic symp- 

 toms and anatomical changes that it is possible clinically or 

 patho-nnatomically to determine what is influenza and what 

 is not. We are here easily involved in a petitio principii: In 

 order to prove that Pfeiffer's bacillus is the microbe of in- 

 fluenza one seeks to show that it occurs regularly in influenza 

 and only in this disease; but in order to judge whether a case 

 of the disease or an epidemic is influenza one must avail 

 oneself of the bacteriological finding! 



By inoculation into animals the etiological significance of 

 the bacillus could not be shown. Pfeiffer worked especially 

 with rabbits, for which it proved strongly toxic without howe- 

 ver multiplying in the animal. By inoculating into the upper 

 air passages of monkeys malaise with fever and some cough 

 could be produced which however could not be described as 

 influenza. 



Pfeiffer's bacillus was first demonstrated in the final stage 

 of the influenza pandemic or perhaps more correctly in the 

 first of the epidemics following the true pandemic which died 

 away in 1890, while influenza again flared up in 1891—92 

 bearing another epidemiological character, that is to say it 

 took the form of isolated epidemics without any mutual con- 

 nection. We may therefore enquire: Was it after all present 

 in the pandemic 1889—90? Pfeiffer tries to prove this by 



