XI. 
BACILLUS OF INFLUENZA. 
DISCOVERED by Pfeiffer (1892) in the purulent bronchial secretion, 
and by Canon in the blood of patients suffering from epidemic in- 
fluenza. Pfeiffer found the bacillus in thirty-one cases examined by 
him, and in uncomplicated cases it was present in the purulent bron- 
chial secretion in immense numbers and in a pure culture. Canon, 
whose independent observations were published at the same time, 
examined the blood of twenty influenza patients in stained prepara- 
tions, and found the same bacillus in nearly all of them. His method 
of demonstrating it is as follows: 
The blood is spread upon clean glass covers in the usual way. 
After the preparations are thoroughly dry they are placed in abso- 
lute alcohol for five minutes. They are then transferred to the fol- 
lowing staining solution (Czenzynke’s): concentrated aqueous solu- 
tion of methylene blue, forty grammes ; one-half-per-cent solution of 
eosin (dissolved in seventy-per-cent alcohol), twenty grammes ; dis- 
tilled water, forty grammes. The cover glasses immersed in this 
staining solution are placed in an incubating oven at 37° C. for from 
three to six hours, after which they are washed with water, dried, 
and mounted in balsam. In successful preparations the red blood 
corpuscles are stained red by the eosin, and the leucocytes blue. The 
bacillusis seen in these as ashort rod, often resembling a diplococcus. 
It is sometimes seen in large numbers, but usually only a few rods 
are seen after a long search—four to twenty in a single preparation. 
In six cases it was found in numerous aggregations containing from 
five to fifty bacillieach. In these cases the blood was drawn during 
a fall of temperature or shortly after. 
Morphology.—Very small bacilli, having about the same diameter 
as the bacillus of mouse septicaemia, but only half as long. Solitary 
or united in chains of three or four elements. 
Stains with difficulty with the basic aniline dyes—best with 
dilute Ziehl’s solution, or Léffler’s methylene blue solution, with heat. 
The two ends of the bacilli are most deeply stained, causing them to 
resemble diplococci. Pfeiffer says: ‘‘I am inclined to believe that 
some of the earlier observers also saw the bacilli described by me, 
but that, misled by their peculiar behavior with regard to staining 
agents, they described them as diplococci or streptococci.” Do not 
stain by Gram’s method. 
