588 Plague 



colonies of Proteus vulgaris. At first these were regarded 

 as contaminations, but later he was led to believe that their 

 occurrence was characteristic of the plague bacillus. The 

 peculiarities of these colonies cannot be recognized after 

 forty-eight hours. 



Gelatin Punctures. In gelatin puncture cultures the 

 development is scant. The medium is not liquefied; the 

 growth takes place in the form of a fine duct, little points 

 being seen on the surface and in the line of puncture. Some- 

 times fine filaments project into the gelatin from the central 

 puncture. 



Abel found the best culture-medium to be 2 per cent, alka- 

 line peptone solution containing i or 2 per cent, of gelatin, 

 as recommended by Yersin and Wilson. 



Agar-agar. Upon agar-agar the bacilli grow freely, but 

 slowly, the colonies being whitish in color, with a bluish tint 

 by reflected light, and first appearing to the naked eye when 

 cultivated from the blood of an infected animal after about 

 thirty-six hours' incubation at 37 C. Under the micro- 

 scope they appear moist, with rounded uneven edges. 

 The small colonies are said to resemble tufts of glass-wool. 

 Microscopic examination of the agar-agar culture shows the 

 presence of chains resembling streptococci. 



Upon glycerin-agar the development of the colonies is 

 slower, though in the end the colonies attain a larger size 

 than those grown upon plain agar. 



Hankin and Leumann* recommended for the differential 

 diagnosis of the plague bacillus a culture-medium prepared 

 by the addition of 2.5 to 3.5 per cent, of salt to ordinary 

 culture agar-agar. When transplanted from ordinary agar- 

 agar to the salt agar-agar, the involution forms so charac- 

 teristic of the bacillus are formed with exceptional rapidity. 

 In bouillon containing this high percentage of salt the stalac- 

 tite formation is beautiful and characteristic. 



Blood-serum. Upon blood-serum, growth, at the tem- 

 perature of the incubator, is luxuriant and forms a moist 

 layer, of yellowish-gray color, unaccompanied by lique- 

 faction of the serum. 



Potato. Upon potato no growth occurs at ordinary 

 temperatures. When the potato is stood in the incubator 

 for a few days a scanty, dry, whitish layer develops. 



*"Centralbl. f. Bakt. u. Parasitenk.," Oct., 1897, Bd. xxn, Nos. 

 16 and 17, p. 438. 



