278 MANUAL OF BACTERIOLOGY. 



as usual. The body of the bacillus is stained pale brown, 

 with dark blue spots, especially at the ends (Fig. 82). 



The diphtheria bacillus is pecuhar in staining irregularly; 

 certain spots stain more sharply than other portions, and 

 darkly stained spots are likely to occur at the ends. It is a 

 facultative anaerobe. It grows most rapidly in the incuba- 

 tor, and slowly, or not at all, below 20° C. Gelatin is not 

 liquefied. It may be cultivated on various alkaline culture- 





•>^.' )«.•,'. ".'I ^4"**^ '^ 



.if'i. 





Fig. 81. — Bacillus OF Diphtheria. (X iooo.} ■' 



media, but grows best on Loffler's blood-serum mixture. 

 On this medium the growth consists of small white or cream- 

 colored, shghtly elevated colonies, which may become con- 

 fluent. The morphology of the bacillus is most character- 

 istic when it is cultivated on blood-serum. It also grows 

 upon glycerin-agar. On potato it produces an invisible 

 growth (see Bacillus of Typhoid Fever). In alkaline bouillon 

 containing dextrose or muscle-sugar the reaction becomes 



