THE BACILLUS OF BUBONIC PLAGUE. 313 



attributed to individual peculiarities of different species 

 of bacteria that were under examination, an opinion 

 that is borne out by more recent studies, from which it 

 has been decided that the genuine plague or pest bacillus 

 does not stain by Gram's method. 



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, transparent, 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 011 the surface and along the 

 track of the needle. Its growth is slow. It does not 

 cause a diffuse clouding of bouillon, but grows rather 

 as irregular, flocculent clumps that adhere to the sides 

 or sink to the bottom of the vessel, leaving the fluid 

 clear. It shows but limited growth on potato. It does 

 not ferment glucose with production of gas, nor does it 

 form indol. It coagulates milk. 



This organism is killed by drying at ordinary room- 

 temperature in four days. It is killed in three or four 

 hours by direct sunlight. It is destroyed in a half hour 

 by 80 C., and in a few minutes by 100 C. (steam). 

 It is killed in one hour by 1 per cent, carbolic acid 

 and in two hours by 1 per cent, milk of lime. 1 



It is pathogenic for rats, mice, guinea-pigs, rabbits, 



1 See " Viability of the Bacillus Pestis," by M. J. Kosenau, U. S. 

 Marine-Hospital Service, Bulletin No. 4, of the Hygienic Laboratory, 

 U. S. M.-H., Washington, D. C., 1901. 



