590 Plague 



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. 



Experimental Infection. Mice, rats, guinea-pigs, rab- 

 bits, monkeys, dogs, and cats are all susceptible to experi- 

 mental inoculation. During epidemics the purely herbiv- 

 orous animals usually escape, though oxen have been known 

 to die of the disease. When blood, lymphatic pulp, or 

 pure cultures are inoculated into them, the animals be- 

 come 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 

 effort, the temperature rises to 41.5 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 seem to suffer from a chronic form of the disease, 

 and sometimes can be found to have encapsulated caseous 

 nodules in the submaxillary glands, caseous bronchial glands, 

 and fibroid pneumonia, months after inoculation. In all 

 such cases virulent plague bacilli are present. 



In and about San Francisco the extermination of rats for 

 the eradication of the plague was unexpectedly complicated 

 by the discovery that other rodents with which the rats came 

 into contact also harbored the plague bacilli. McCoy and 

 Smith f found this to be true of the prairie dog, the desert 

 wood rat, the rock squirrel, and the brush rat. To insure 

 security against the recurrence of the disease among men 

 necessitates continued observation of these animals and the 

 extermination of diseased colonies, as well as their complete 

 extermination in the neighborhood of human habitations. 



According to Yersin, 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 yellow- 

 ish gelatinous exudation. The spleen and liver are enlarged, 

 the former often presenting an appearance similar to that 



* "Arbeiten aus d. Kaiserl. Gesundheitsamte," 1901, xvm. 

 t "Journal of Infectious Diseases," 1910, vn, p. 374. 



