178 BUBONIC PLAGUE. 



prostration and delirium, and the occurrence of lymphatic 

 swellings (buboes) affecting chiefly the glands corresponding 

 to the inoculated portion. These become very much enlarged, 

 and have a tendency to soften and suppurate. In severe 

 cases death occurs in forty-eight hours ; in others, the dura- 

 tion of the disease is somewhat longer. The prognosis is 

 more favorable, the longer the duration of the disease. Char- 

 acteristic bacilli are found in the lymphatic glands, and also 

 occasionally in the blood. 



Immunity. Persons who have recovered from an attack of 

 bubonic plague or animals that have survived inoculations 

 are found to be immune for a certain period of time. This 

 immunity is due to a substance developed in the serum of 

 those animals, which may also when inoculated into suscepti- 

 ble animals protect them from infection with bubonic plague. 

 Artificial immunity may also be conferred by injecting cult- 

 ures of the dead bacilli. 



Agglutination. The serum of immune animals possesses 

 also an agglutinating action when mixed with bouillon cult- 

 ures of the Bacillus pestis, very much the same as the agglu- 

 tinative action of typhoid or cholera serum. 



Serotherapeutics. Yersin claims to have developed a serum 

 in the horse which is not only protective, but also curative, 

 when injected into the human being. His experiments, 

 carried on in a number of cases, seem to indicate this serum 

 to have some decided beneficial effect when administered early 

 in the disease, the proportion of deaths in cases so treated 

 being scarcely 8 per cent., whereas the mortality in non- 

 inoculated cases is as high as 80 per cent. To obtain the 

 blood-serum from horses, he immunizes them with the dead 

 bouillon cultures of the Bacillus pestis. 



Haffkine has practised on an extensive scale protective in- 

 oculations against bubonic plague by injections of dead cult- 

 ures. This immunity seems to last for several weeks. 



Recently, observations have demonstrated that Yersin 

 serum has absolutely no protective or curative properties. 

 Haffkine's protective inoculations are still held in favor, 

 however. 



