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drop-like cultures may be seen along the line of inocula-
tion. They do not look unlike condensed moisture, and
Kitasato makes a special point of the fact that the colo-
nies never become confluent. The colonies may at times
be so small as to require a lens for their discovery.
In bouillon a scant development occurs, small whitish
particles appearing upon the surface, subsequently sink-
ing to the bottom and causing a "woolly" deposit there.
While the growth is so delicate in these ordinary media,
the bacillus grows quite well upon culture-media contain-
FIG. 126.—Bacillus of influenza ; colonies on blood agar-agar; low magnifying
ing hemoglobin or blood, and can be transferred from
culture to culture many times before it loses its vitality.
It cannot be positively proven that this bacillus is the
cause of influenza, but from the fact that the bacillus
can be found only in cases of influenza, that its presence
corresponds with the course of the disease in that it is
present as long as the purulent secretions last, and then
disappears, and that Pfeiffer was able to demonstrate its
presence in all cases of uncomplicated influenza, his con-
clusion that the bacillus is specific is certainly justifiable.