EPIDEMIOLOGY OF INFLUENZA 



495 



0.2 to 0.3 micron in width. They are somewhat irregular in length, 

 but show rounded ends. They rarely form chains. They are non- 

 motile, and do not form spores. 



Influenza bacilli stain less easily than do most other bacteria 

 with the usual anilin dyes, and are best demonstrated with 10 per 

 cent aqueous fuchsin (5 to 10 

 minutes), or with Loeffler's methy- 

 lene-blue (5 minutes). They are 

 Gram-negative, giving up the 

 anilin-gentian voilet stain upon 

 decolorization. Occasionally slight 

 polar staining may be noticed. 

 Grouping, especially in thin smears 

 of bronchial secretion, is charac- 

 teristic, in that the bacilli very 

 rarely form threads or chains, 

 usually lying together in thick, 

 irregular clusters without definite 

 parallelism. 



Isolation and Cultivation. Iso- 

 lation of the influenza bacillus is 

 not easy. Pfeiffer 24 succeeded in 

 growing the bacillus upon serum- 

 agar plates upon which he had 

 smeared pus from the bronchial 

 secretions of patients. Failure of growth in attempted subcultures 

 made upon agar and gelatin, however, soon taught him that the 

 success of his first cultivations depended upon the ingredients of 

 the pus carried over from the sputum. Further experimentation 

 then showed that it was the blood, and more particularly the 

 hemoglobin, in the pus which had made growth possible in the 

 first cultures. Pfeiffer made his further cultivations upon agar, 

 the surface of which had been smeared with a few drops of blood 

 taken sterile from the finger. Hemoglobin separated from the red 

 blood cells was found to be quite as efficient as whole blood. Whole 

 blood taken from the finger may be either smeared over the surface 

 of slants or plates, or mixed with the melted meat-infusion agar. 

 In isolating from sputum, only that secretion should be used which 



FIG. 49. BACILLUS INFLUENZA ; Smear 

 from pure culture on blood agar. 



Pfeiffer, loc. cit. 



