PNEUMONIA AND DIPHTHERIA. 229 



slightly pointed off towards its free ends.^ It is not 

 merely a miorooocous, but a very short bacillus. Oc- 

 casionally also little threads consisting of from four 

 to eight cells are found. In the animal body this 

 organism, like the pneumococcus, develops a fairly thick 

 capsule, which never occurs in the artificially cultivated 

 specimens. In the matter of staining, there is not 

 much difference between this bacterium and the pre- 

 ceding one ; but as it is not decolourised when treated 

 according to Gram's method, they may be easily dis- 

 tinguished from one another by this means. 



In cultures, Prankel's Diplococcus pneurnonice ex- 

 hibits very marked peculiarities. It is very difiScult 

 to cultivate, and hence the greatest attention is 

 necessary. First it requires a slightly alkaline medium ; 

 it is very susceptible to the least variation in the re- 

 action of its medium. If this contains the smallest 

 trace of free acid, the cultivation is a complete failure. 

 Further, the temperature must not sink below 24° ; 

 it grows most quickly and luxuriantly at a tempera- 

 ture of 37°. Hence it can only be cultivated on at 

 least ] 5/^ gelatine, which must be kept at about 24°, 

 since if only a slight rise of temperature occurs, the 

 geUtine commences to liquefy. On gelatine plates 

 very small transparent colonies with sharp outlines 

 are formed ; these only grow slowly, arid never attain 

 to any great size. The gelatine is never liquefied. 

 In gelatine puncture cultures, colonies like those of 



