PLAGUE AND BACILLUS PESTIS 800 



staining of the polar portions of the bacillus is usually easy to 

 demonstrate. Special polar stains have been devised by various 

 observers. Most of these depend upon avoidance of the usual heat 

 fixation of the preparations, which, in some way, seems to interfere 

 with good polar staining. Fixation of the dried smears with absolute 

 alcohol is, therefore, preferable. The bacillus is decolorized by 

 Gram's method. 



Isolation and Cultivation. The bacillus is easily isolated in pure 

 culture from the specific lesions of plague patients, during life or at 

 autopsy. It is worth noting that smears from bubos and other 

 plague lesions will often show the typical bacilli in very small 



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> 



FIG. 86. BACILLUS PESTIS, 'INVOLUTION FORMS. (After Zettnow.) 



numbers only, possibly because of the ease with which they 

 undergo degeneration. The bacillus grows readily and luxuriantly 

 upon the meat-infusion media. The optimum temperature for its 

 cultivation is about 30 C. Below 20 C. and above 38 C., growth 

 is sparse and delayed, though it is not entirely inhibited until 

 exposed to temperatures below 12 C., or above 40 C. The most 

 favorable reaction of culture media is neutrality or moderate al- 

 kalinity, though slight acidity does not prevent development. 



On agar, growth appears within twenty-four hours as minute 

 colonies with a compact small center surrounded by a broad, 

 irregularly indented, granular margin. 



