Pfeiffer1 found influenza bacilli in all fresh uncomplicated cases of influenza in almost pure culture. His investigation was carried out for the most part on persons seeking hospital care for the more severe attacks of bronchitis and bronchopneumonia. Influenza bacilli were found only in influenza patients with and convalescent from influenza, a fact of great importance in Pfeiffer's opinion in establishing the specific nature of the organism. In three cases of bronchopneumonia complicating diphtheria, organisms closely resembling influenza bacilli were found but somewhat larger and with an outspoken tendency to the formation of longer thread forms. Such organisms he called pseudo-influenza bacilli.
Subsequent workers have failed to confirm the presence of a group of pseudo-influenza bacilli. Such differences as Pfeiffer described are to be regarded as variations in morphology in different generations and on different culture mediums.
In the period immediately following the great pandemic of 1889-1890, and subsequent
LORD FT, SCOTT AC, NYE RN. RELATION OF INFLUENZA BACILLUS TO THE RECENT EPIDEMIC OF INFLUENZA. JAMA. 1919;72(3):188–190. doi:10.1001/jama.1919.02610030034013
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