658 BACTERIA OF THE RESPIRATORY TRACT 



It occurs almost constantly in whooping cough and very commonly in measles, tuber- 

 culosis, influenzas and catarrhs, varicella, bronchitis, meningitis, lobar pneumonia, 

 pharyngitis, and sinus infections. In the terminal conditions, especially pneumonias 

 of these different infections, it is common and abundant. On the whole, it appears to 

 be more numerous in the respiratory tract in pathological states than in normal states. 



Summing up the evidence at hand from the extensive studies made before, dur- 

 ing and after the last epidemic, we may conclude fairly that no specific differences 

 have been made out between the bacilli in the various respiratory infections, includ- 

 ing epidemic influenza. As stated, all attempts by different workers to make out a 

 definite epidemic strain of influenza bacilli as the cause of the influenza epidemic have 

 failed. And the slight differences already noted — cultural, morphological, and sero- 

 logical — existing between strains are not known to indicate specificity for a given dis- 

 ease. This point should be emphasized. Because of the prevalence and the very wide 

 distribution of Pfeiffer's bacillus in normal persons and in those suffering with a great 

 variety of respiratory infections, studies upon the incidence of this organism are not 

 of great value in any attempt to determine its relation to a given infection or epidemic. 

 This point was responsible for many erroneous conclusions that have been drawn in 

 connection with earlier studies. 



The impression should not be gained that, because the evidence is decidedly a- 

 gainst the existence of epidemic strains of PfeifTer's bacillus, it is a relatively harmless 

 organism. No better example need be given than the occurrence of the so-called "in- 

 fluenza meningitis," caused by pure growths of this bacillus; 90 per cent of these cases 

 are fatal. And it may cause endocarditis, pericarditis, pleuritis, arthritis, and other 

 infections from whose lesions the bacillus may be grown pure. Experimentally, too, 

 for both humans and animals, it may have distinct pathogenic powers. In the human, 

 inoculation with pure cultures will at times cause a definite infection.^ But no one 

 has reproduced a clinical picture that could be called typical influenza. 



We may say, then, that the influenza bacillus of Pfeiffer is one of our common 

 throat bacteria found in a high percentage of persons at any time and often in large 

 numbers. It is found more frequently and in larger numbers in respiratory infections. 

 No convincing evidence exists that it is the primary cause of pandemics of influenza 

 or of any other respiratory epidemics. It requires for its existence not only the or- 

 dinary constituents of media, but also the presence of a vitamine or vitamine-like 

 Ijody. 



EPIDEMIOLOGICAL PROBLEMS 



Before concluding, mention should be made of the numerous epidemiological 

 problems that present themselves in dealing with bacteria of the respiratory passages. 

 Many of these problems remain at the present time extremely obscure and furnish 

 some baffling phenomena. Many respiratory bacteria are opportunists, and because 

 of a long association and close adaptation their relation and behavior to the host are 

 complicated and difficult to analyze and understand. Our great respiratory epidemics 

 appear suddenly, and vvc are as helpless before them today as were the people hun- 



• Davis, 1). J.: J . InUrl. Dis., 3, i. igo6. 



