INFLUENZA BACILLUS. 323 
eighteen hours and then examined under a magnifica- 
tion of about 100 diameters. The influenza colonies, 
when present, will be found in the neighborhood of 
the blood-cells, much lighter in hue, somewhat smaller, 
and more finely granular than those of the pneumococci. 
They appear scarcely more noticeable than the groups of 
blood-cells that have lost their color and largely disin- 
tegrated. With higher magnification the colonies do not 
show the individual bacteria distinctly, and thus con- 
trast with the pneumococci. The suspicious colonies are 
fished out, inoculated upon blood and simple nutrient 
agar, and examined microscopically. When the detec- 
tion of the bacilli is important, and there are any puru- 
lent masses in the sputum, as in influenza complicating 
phthisis, these are washed, as under directions for ex- 
amination of sputa for mixed infection (page 306). 
On 1.5 per cent. sugar-agar growth also occurs, the 
colonies appearing as extremely small droplets, clear 
as water, often only recognizable with a lens (Pfeiffer). 
In bouillon a very scanty development takes. place, un- 
less blood is added. At the end of twenty-four hours 
small, white particles are seen on the surface, which 
subsequently sink to the bottom, forming a white, 
woolly deposit, while the bouillon remains clear. 
REsISfANCE AND LENGTH OF Lire. The influenza 
bacillus is very sensitive to desiccation; a pure culture 
diluted with water and dried is destroyed with certainty 
in twenty-four hours; in dried sputum the vitality, 
according to the completeness of drying, is retained 
from twelve to forty-eight hours. It does not grow, 
but soon dies in water. The thermal death-point is 
60° C. with five minutes’ exposure (Pfeiffer and Beck). 
In bouillon cultures and in sputum at 20° C. they retain 
