PLAGUE. 201 



Appearance in Culture. On gelatin-plates the colonies 

 appear as finely granular bodies of brownish color, with a 

 smooth border. The superficial colonies possess a delicate mar- 

 ginal zone. The culture-medium is not liquefied. 



In gelatin stab-cultures slow, uniform growth takes place along 

 the line of inoculation, while a smooth deposit forms upon the 

 surface. 



In gelatin streak-cultures a light yellowish deposit forms. 



On agar-plates, after twenty-four hours, delicate, dewdrop-like 

 colonies form that appear, after the lapse of forty-eight hours, 

 as grayish points, whose border is slightly iridescent. At times 

 a number of large colonies are seen among the smaller. 



In agar stab-cultures a tough, mucoid coating develops, the 

 water of condensation is rendered turbid, but no membrane forms. 



In Loffler 1 s blood-serum the same development takes place as 

 in agar streak-cultures. 



Bouillon is rendered diffusely turbid. If, however, it be in- 

 oculated with a coherent bacterial mass from an agar-culture, 

 the bacilli develop at the bottom of the tube, while the over- 

 lying fluid remains clear. In this way a growth is obtained that 

 is suggestive of streptococci. 



Milk is a poor culture-medium, and is not coagulated. 



Upon potatoes a scanty, whitish-gray coating forms at a tem- 

 perature of 37 C. (98.6 F.). 



In culture-media containing sugar the plague-bacillus does 

 not generate gas. It does not form indol either in bouillon or in 

 peptone-water. 



Wladimiroff and Kressling believe a neutral reaction of the 

 culture-medium most favorable for growth. Addition of glycerin 

 to the nutrient medium is rather disadvantageous. 



Vital Capability of Plague-bacilli. Exposure for ten 

 minutes to a temperature of 55 C. (131 F. ) or for five min- 

 utes to a temperature of 80 C. (176 F.) suffices to cause the 

 death of the bacilli. They are destroyed at once by a i : 1000 

 solution of mercuric chlorid, and in ten minutes by one per 

 cent, carbolic acid or one per cent, lysol. Mineral acids are 

 very active : Sulphuric acid, i : 2000, destroys the bacilli within 

 five minutes ; hydrochloric acid, i : 1000, within thirty min- 

 utes. When material containing plague-bacilli was transferred 

 to linen, wool,, earth, etc., the longest period for which life was 

 preserved was eight days. The same observation was made with 

 regard to preserved portions of organs. The sputum from 

 cases of pneumonia complicating plague, kept in tubes closed 

 with cotton, was no longer infective after sixteen days. In or- 

 dinary tap-water the bacilli die 'in three days, in sterilized water 

 in eight days, in sterilized bilge-water after five days (German 

 Plague-commission). 



