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 aerobic and facultative anaerobic; 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 



