5 so Plague 



, Wilson* found the thermal death-point 'of the organism one or 

 two degrees higher than that of the majority of non-sporulating 

 pathogenic bacteria, and that the influence of sunlight and desicca- 

 tion cannot be relied upon to destroy it. 



Rosenauf found temperature the most important factor, as it 

 dies quickly when kept dry at 37°C., but remains alive for months 

 when kept dry at i9°C. Sunlight kills it in a few hours. A tem- 

 perature of 7o°C. is invariably fatal in a short time. 



Metabolism. — The bacillus develops best under aerobic con- 

 ditions though it develops to a slight extent also under anaerobic 

 conditions. In glucose-containing media it does not form gas. 

 No indol is formed. Ordinarily the culture-medium is acidified, 

 the acid reaction persisting for three weeks or more. 



Ghon,J Wernicke, § and others who have studied the toxic 

 products of the bacillus all incline to the belief that it forms only 

 endotoxin. 



Kossee and Overbeck,|| however, believe that there is, in addition, 

 a soluble exotoxin that is of importance. 



Bielonovsky** finds that broth, agar, and serum cultures of the 

 plague bacillus possess the property of hemolyzing the blood of 

 normal animals. The hemolytic power of filtrates of plague cultures 

 increases up to the thirteenth or fourteenth day, then gradually di- 

 minishes, but without completely disappearing. The hemolysins 

 are notably resistant to heat, not being destroyed below ioo°C. 



Experimental Infection. — Mice, rats, guinea-pigs, rabbits, and 

 monkeys are all susceptible to experimental inoculation. When 

 blood, lymphatic pulp, or pure cultures are inoculated into them, 

 the animals become ill in from one to two days, according to their 

 size and the virulence of the bacillus. Their eyes become watery, 

 they show disinclination to take food or to make any bodily efiort, 

 the temperature rises to 4i.5°C., they remain quiet in a corner of 

 the cage, and die with convulsive symptoms in from two to seven 

 days. If the inoculation be made intravenously, no lymphatic 

 enlargement occurs; but if it be made subcutaneously, the nearest 

 lymph nodes always enlarge and suppurate if the animal live long 

 enough. The bacilli are found everywhere in the blood, but not in 

 very large numbers. 



Rats suffer from both an acute septicemic and a chronic form of 

 the disease. In the former an infiltration or watery edema can be 

 observed in a few hours about the point of inoculation. The autopsy 

 shows the infiltration to be made up of a yellowish gelatinous exuda- 



* "Journal of Medical Research," July, igoi, vol. vi, No. i, p. 53- 



t Bulletin No. 4 of the Hygienic Laboratory of the U. S. Marine Hospital 

 Service, 1901. 



t Wien, 1898. 



§ "Centralbl. f. Bakt.," etc., 1898, xxrv. 



I "Arbeiten aus d. Kaiserl. Gesundheitsamte," 1901, xviii. 

 , ** "Arch, des Sci. Biol.," Petersb., 1904. St. Tome x, No. 4. 



