INFLUENZA. 281 



INFLUENZA. 



On the first occurrence of influenza in the winter of 

 1889 90 the numerous bacteriologic investigations under- 

 taken failed to yield conclusive results. In the secretions 

 of influenza-patients the ordinary exciting agents only of 

 inflammation, especially streptococci and lanceolate diplo- 

 cocci, were encountered. Of the latter it was stated that in 

 appearance and growth they presented certain points of 

 distinction as compared with ordinary pneumococci. A 

 specific bacterium was, however, not found. In subsequent 

 epidemics (1891 and 1892) Pfeiffer, in the Hygienic Institute 

 at Berlin, recognized a special bacillus as the exciting agent 

 of influenza, and developed it in pure culture. The state- 

 ments of Pfeiffer have since been completely confirmed. 



Morphology of the Influenza-bacillus. The influenza- 

 bacillus is an extremely small organism (0.2 // thick and 

 0.5 fj. long), in thickness not quite equaling the slender bacilli 

 of mouse-septicemia, and being only twice or thrice as long as 

 wide. Its extremities are rounded. Rarely in the sputum and 

 more commonly in recent pure culture, the bacilli form short 

 pseudo-filaments. Long bands in cultures three or four days 

 old are to be considered as beginning involution-manifestations. 

 The influenza-bacilli possess no capsule, and are without move- 

 ment of their own. Frequently, two especially short bacilli lie 

 close to each other (division-forms). This may readily give 

 rise to confusion with diplococci. 



Influenza-bacilli appear not to possess spores. Spore-like 

 formations have never been found in the secretions or in cul- 

 tures, and, besides, the bacillus is but little .resistant to the influ- 

 ence of temperature, drying, etc. 



Staining of Influenza-bacilli. The bacilli take the stain 

 with considerable difficulty. Loffler's solution of methylene- 

 blue may be employed, and, still better, a dilute, pale-red solu- 

 tion of carbolfuchsin in water. The preparation must be ex- 

 posed to the action of the stain for from five to ten minutes. 

 If the exposure is of shorter duration, or if other stains are 

 employed, the central portion of the bacillus is often more 

 feebly stained than the extremities. The bacilli are not stained 

 by Gram's method. 



Cultivation of the Influenza-bacillus. The influenza- 

 bacillus is strictly aerobic, and it develops only in the presence 

 of hemoglobin or of leukocytes. The latter fact explains why 

 cultivation of the influenza-bacilli remained for so long a time 



