232 PRACTICAL BACTERIOLOGY. 



tares, or if we wish to demonstrate the presence of the 

 bacilli in false membraaes. Gram's method is quite 

 useless for the diphtheria bacillus, for it either becomes 

 quite decolourised, or only a very small portion in the 

 interior of the cell remains faintly stained. Even 

 the other staining solutions are not suitable, for the 

 bacilli, already so varying in their shape, become still 

 more changed by powerful staining reagents. 



These bacilli only develop at a temperature of 

 over 20°. If the same gelatine is used as for the 

 Diplococcus pneumoniae, there appear on the culture 

 plates small disc- shaped, whitish colonies, which are 

 seen with the microscope to have slightly jagged 

 edges. Upon agar-agar cultivations kept at blood 

 heat thin transparent coatings are at first formedj these, 

 to begin with, only grow veiy slowly, but gradually 

 they develop more rapidly as the bacteria evidently 

 grow more accustomed to their soil. In agar-agar 

 plate cultivations, which have been kept ^t blood heat 

 for two days large colonies appear, which are about 

 the size of pins'-heads ; they are flat and lenticular in 

 shape, and of a greyish white colour ; when they reach 

 the surface they are very glistening and more trans- 

 parent. If such a colony is examined with a low 

 power, a very characteristic appearance may be 

 observed. The small colonies with their irregular out- 

 lines look like an innumerable quantity of rough 

 granules packed closely together. Amongst the better 



