PATHOGENIC BACTERIA. 



339 



Stain the cover-glass preparation which has been fixed in the 

 flame in No. i one to three seconds; wash in water; stain in No. 

 2 three to five seconds; wash in water; mount as usual. The 

 body of the bacillus is stained pale brown, with dark blue spots, 

 especially at the ends (Fig. 87). In regard to the Gram scain, 

 some strains retain the stain while others do not. Hamilton 

 and Horton* found that of '18 cultures isolated by them, 11 

 were Gram negative, 7 were Gram positive. 



Fig. 86. — Bacillus of diphtheria. (X looo.) 



The diphtheria bacillus is peculiar 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 incubator, 

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

 It may be cultivated on various alkaline culture-media, but 

 grows best on Lofl9er's blood-serum mixture (page 75). On this 

 *Journ. Inject. Dis. Vol. III. 1906. p. 132. 



