500 BACTERIOLOGY. 
from which they are obtained. As observed in the 
blood of inoculated animals it is usually in pairs of 
lancet-shaped elements, which are surrounded by a cap- 
sule. (See Fig. 65.) When grown on culture media 
longer or shorter chains are frequently formed, which 
can scarcely be, or even not at all, distinguished from 
_ chains of streptococci. The individual cells are almost 
spherical in shape, and they are rarely surrounded by 
a capsule. (See Fig. 66.) 
The capsule is best seen in stained preparations from 
the blood and exudates of fibrinous pneumonia or from 
the blood of an inoculated animal, especially the mouse, 
in which it is commonly, though not always, present. 
It is seldom seen in preparations from cultures. 
It stains readily with ordinary aniline colors; it is 
not decolorized after staining by Gram’s method. The 
capsule may be demonstrated in blood or sputum either 
by Gram’s or Welch’s (glacial acetic acid) method. 
Biological Characters. It grows on almost all the 
culture media ordinarily employed, but its suscepti- 
bility is shown not only by its irregularity of form, but 
also by its slow and comparatively scanty growth and 
by its rapid loss of virulence and power of reproduction 
under varying conditions. It grows equally well in 
the absence as in the presence of oxygen, being thus 
both aérobic and facultative anaérobic; its parasitic 
nature is exhibited by the short range of temperature 
at which it grows—viz., from 25° to 42° C.—its maxi- 
mum growth being at about 37° C., or the temperature 
of the body. Its thermal death-point, as determined 
by Sternberg, is 52° C., the time of exposure being 
ten minutes. It loses its vitality in cultures in a 
comparatively short time, and is very sensitive to the 
