NOTWITHSTANDING a large number of bacteriologic
examinations conducted for the purpose of determining
the cause of influenza, it was not until 1892, after the
great epidemic, that there was found simultaneously by
Canon and Pfeiffer a bacterium which conformed, at least
in large part, to the requirements of specificity.
The observers mentioned found the same organism—
one in the blood of influenza patients, the other in the
purulent bronchial discharges.
The specific organisms (Fig. 125) are bacilli, very small
in size, having about the same diameter as the bacillus
FIG. 125.—Bacillus influenzse, from a gelatin culture; x 1000 (Itzerott and
of mouse-septicemia, but only about half as long (0.2 by
0.5 fjL). They are usually solitary, but may be united in
chains of three or four elements. They stain rather