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. 



EESISTANCE AND LENGTH OF LIFE. 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 



