BACILLUS OF BUBONIC PLAGUE 197 



Spore Formation. Absent. 



Staining Reactions. Exhibits polar staining with the ordinary 

 staining methods (see Photomicrograph, Plate IV., Fig. 20) ; does not 

 stain by the Gram method, although Kitasato says at one time it stains 

 by the Gram method, and at another time it is discolorized ; but as 

 mixed infection is often present, the above peculiar reaction towards 

 the Gram stain can perhaps be attributed to other species of bacteria. 



Biological Characters. The bacillus grows best between 36 and 

 39 C., but also develops very well at ordinary room temperature. 



On Gelatine Plates. Small darkly-defined granular colonies of a 

 brownish colour occur, and the medium is not liquefied. 



In Gelatine Stab Cultures. It develops slowly on the surface, and 

 along the track of the needle. 



On Agar Plates. In twenty-four hours small dewdrop-like colonies 

 appear, which in forty-eight hours resemble grey beads with slightly 

 iridescent borders ; sometimes a large colony is observed between the 

 smaller ones. The deep colonies are round and granular. 



On oblique surface Agar a viscous shiny coating appears ; the above- 

 mentioned colonies like dewdrops being sometimes observed. The 

 water of condensation is clouded, but there is no film formed. (See Photo- 

 graph, Fig. 77.) 



The growth on blood serum is similar to that on ordinary agar. 



Bouillon becomes diffusely clouded, but if it is inoculated with a 

 cohesive mass of bacteria from an agar culture, the bacilli develop on 

 the bottom of the tube, while the upper portions of the medium remain 

 clear ; this mode of growth being somewhat similar to that of strepto- 

 cocci. 



Milk is a bad medium, and is not coagulated. 



Potatoes. On the surface at 37 C. a scanty greyish-white growth 

 occurs. 



The bacillus of bubonic plague forms no gas in sugar - containing 

 media, and no indol in either bouillon or peptone water. It grows best 

 on media of neutral reaction (Wlademiroff and Kressling). The addi- 

 tion of glycerine to the media is detrimental. 



Vitality of the Bacillus of Bubonic Plague. It is killed by 

 heating ten minutes at 55 C., and five minutes at 80 C. Corrosive 

 sublimate 1 to 1000 destroys the bacilli immediately ; 1 per cent, carbolic 

 acid and 1 per cent, lysol in ten minutes. The mineral acids are very 

 effective. Sulphuric acid 1 to 2000 kills the bacilli in five minutes. Hydro- 

 chloric acid 1 to 1000 in thirty minutes. The longest time that infected 

 material on lint, wadding, earth, etc., remained active was eight days. 

 Sputum from patients affected with the pneumonic form kept in a vessel 

 plugged with cotton wool, was no longer virulent in sixteen days. In 

 ordinary drinking water the bacilli die in three days, in sterilized water 



