372 APPLICATION OF METHODS OF BACTERIOLOGY 



Kong, China; although since then numerous other inves- 

 tigators have made additional important contributions to 

 our knowledge of the subject. The results of these studies 

 demonstrate that bubonic plague is an infectious, not 

 markedly contagious disease (except in the case of the 

 pulmonic variety), that depends for its existence upon the 

 presence in the tissues of a specific micro-organism — the 

 so-called plague or pest bacillus. 



This organism is described as a short, oval bacillus, usually 

 seen single, sometimes joined end to end in pairs or threes, 

 less commonly as longer threads. It stains more readily 

 at its ends than at its centre. It is sometimes capsulated; 

 is non-spore-forming; is aerobic, and is non-motile. It is 

 found in large numbers in suppurating glands. (Fig. 73.) 

 It is also to be detected in the blood, spleen, lungs, liver, 

 kidneys, walls of the stomach and intestines, urine, and 

 intestinal contents of fresh cadavers; and during life in the 

 blood, expectorations, feces, and urine of persons sick of the 

 disease. From these findings the infection is obviously a 

 septicemia. 



It is negative to the Gram method but stains readily with 

 the ordinary aniline dyes. It may be cultivated upon 

 ordinary nutrient media, although preference is given by 

 some to a neutral or slightly alkaline 2 per cent, peptone 

 solution containing from 1 to 2 per cent, of gelatin. 



The most favorable temperature for its growth is between 

 36° and 39° C. Its colonies on glycerin-agar-agar and on 

 coagulated blood-serum are described as iridescent, trans- 

 parent, and whitish. On gelatin at 18°-20° C. it develops 

 as small, sharply defined, white colonies without liquefaction 

 of the medium. In stab-cultures it develops both on the 

 surface and along the track of the needle. Its growth is 



