350 



BACTERIA PATHOGENIC TO MAN 



organism, there being great differences according to the source from 

 which they are obtained. As observed in the sputum and blood it is 

 usually in pairs of lancet-shaped elements, which are surrounded by a 

 capsule. (See Fig. 108.) When grown in fluid culture media longer or 

 shorter chains are frequently formed, which can scarcely be distin- 

 guished from chains of certain streptococci, except that, as a rule, the 

 length of the chain is less and the pairs of diplococci are farther apart. 

 In cultures the individual cells are almost spherical in shape, and 

 except in certain varieties are rarely surrounded by a capsule. (See 

 Fig. 109.) The pneumococcus is by some classed as a streptococcus. 



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 



FIG. 108 



FIG. 109 





*4lr 



$."* 





Diplococcus of pneumonia from blood, with sur- 

 rounding capsule stained by method of Hiss. 



Pneumococcus from bouillon culture, 

 resembling streptococcus. 



always, present. It is seldom seen in preparations from cultures unless 

 special media are employed. Flagella are not present. 



Staining. 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, or the copper sulphate method of Hiss. 



Biology. It grows equally well with or without oxygen, being thus 

 both aerobic and facultative anaerobic; its parasitic nature is exhibited 

 by the short range of temperature at which it usually grows viz., from 

 25 to 42 C. best at 37 C. In the cultivation of this organism 

 neutral or slightly alkaline media should be employed. The organism 

 grows feebly on the serum-free culture media ordinarily employed for 

 the cultivation of bacteria viz., on nutrient agar and gelatin, in 

 bouillon. The best medium for its growth is a mixture of one-third 



