464 BACILLUS OF INFLUENZA. 
Biological Characters.—An aérobic, non-motile bacillus. Does 
not grow in nutrient gelatin at the room temperature. Spore forma- 
tion not observed. Upon thesurface of glycerin-agar in the incubat- 
ing oven very small, transparent, drop-like colonies are developed at 
the end of twenty-four hours. These can only be recognized by the 
aid of alens. ‘‘A remarkable point about them is that the colonies 
always remain separate from each other, and do not, as all other 
species known to me do, join together and form a continuous row. 
This feature is so characteristic that the influenza bacilli can be 
thereby with certainty distinguished from other bacteria ” (Kitasato). 
On 1.5 per cent sugar-agar the colonies appear as extremely small 
droplets, clear as water, often only recognizable with a lens 
(Pfeiffer). 
In bourlion a scanty development occurs, and at the end of twen- 
ty-four hours small, white particles are seen upon the surface, which 
subsequently sink to the bottom, forming a white, woolly deposit, 
while the bouillon above remains transparent. This bacillus does 
not grow at temperatures below 28° C, 
Canon has obtained colonies, resembling those described by Kita- 
sato, in cultures from the blood of influenza patients. His cultures 
were made upon glycerin-agar in Petri’s dishes. Tenor twelve drops 
of blood from a puncture made in the finger of the patient, after 
sterilization of the surface, were allowed to fall upon the agar medium, 
and this was placed in the incubating oven. As the number of ba- 
cilli in the blood is small, a considerable quantity is used. The 
colonies are visible at the end of twenty-four to forty-eight hours. 
The influenza bacillus is quickly destroyed by desiccation; a 
pure culture diluted with water and dried is destroyed with cer- 
tainty in twenty hours; in dried sputum the vitality is retained 
somewhat longer, but no growth occurs after forty hours. The 
thermal death-point is 60° C. with five minutes’ exposure (Pfeiffer 
and Beck). 
Pathogenesis.—Pfeiffer infers that this is the specific cause of 
influenza in man for the following reasons : 
1. They were found in all uncomplicated cases of influenza ex: 
amined, in the characteristic purulent bronchial secretion, often in 
absolutely pure cultures. They were frequently situated in the pro- 
toplasm of the pus corpuscles ; in fatal cases they were found to 
have penetrated from the bronchial tubes into the peribronchitic tis- 
sue, and even to the surface of the pleura, where in two cases they 
were found in pure cultures in the purulent exudation. 
2. They were only found in cases of influenza. Numerous con- 
trol experiments proved their absence in ordinary bronchial ca 
tarrh, etc. 
