CHAPTER XXIII 
THE INFLUENZA GROUP. THE BACILLUS PER¬ 
TUSSIS. BACILLUS PESTIS. THE CHOLERA 
GROUP. THE BACILLUS OF DUCREY 
The Influenza Group 
Until the last epidemic, or rather, pandemic of influ¬ 
enza, it was customary to regard the Pfeiffer’s Bacillus 
as the cause of influenza, but today, in the light of the 
enormous amount of work done since the last epidemic, 
it seems that the great mortality (almost always due to 
bronchopneumonia) during epidemics is due to some or¬ 
ganisms in addition to B. Influenzas, most probably strep¬ 
tococci and pneumococci. 
Pfeiffer’s Bacillus Influenzas is an extremely small 
organism (0.5 micron) noncapsulated, possessing no 
spores and no flagella. They do not stain very well 
with the ordinary aniline dyes, and the best stain is 
fuchs:‘ne (10 per cent) or Loeffler’s methylene blue—al¬ 
lowed to act about 5-7 minutes. 
The best culture medium for the cultivation of the 
influenza bacilli is either the blood agar, Avery’s sodium 
oleate blood medium (Jour. Am. Med. Assn., 1918, vol. 
71) or Park and Williams special influenza medium. 
The cultures are very sensitive to changes in the tem¬ 
perature and are very short-lived, requiring transfers 
every 3 or 4 days. The endotoxins of the Pfeiffer’s 
bacillus are very powerful. 
Between the epidemics this organism is found in the 
upper respiratory tract, and apparently bears no rela- 
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