BUBONIC PLAGUE. 441 



the influence of sunlight and desiccation cannot be relied 

 upon to limit its viability. 



Kitasato's experiments first showed that it is possible 

 to bring about immunity to the disease, and Yersin, 

 working in India, and Fitzpatrick, in New York, have 

 successfully immunized large animals (horses, sheep, 

 goats). The serum of these immunized animals con- 

 tains an antitoxin capable not only of preventing the dis- 

 ease, but also of curing it in mice and guinea-pigs and 

 probably in man. 



HafFkine in his experiments followed the line of pre- 

 ventive inoculation as employed against cholera. Bouil- 

 lon cultures were used in which floating drops of butter 

 were employed to make the islands of plague bacilli 

 float. The cultures were grown for a month or so, suc- 

 cessive crops of the island-stalactite growth as it formed 

 having been precipitated by agitating the tube. In this 

 manner there was obtained an "intense extra-cellular 

 toxin" containing large numbers of the bacilli. The 

 culture was killed by exposure to a temperature of 70 

 C. for one hour, and the mixture used in doses of about 

 3 c.cm. as a preventive inoculation. In the Byculla 

 Gaol, where Haffkine's experiments numbered over one 

 hundred, a decided prophylactic effect was observed in 

 twelve to fourteen hours in men already advanced in the 

 stage of incubation. 



Wyssokowitz and Zabolotmy, whose studies have 

 already been quoted, used 96 monkeys in the study of 

 the value of the "plague-serums," and found that 

 when the treatment is begun within two days from the 

 time of inoculation the animals can be saved, even 

 though symptoms of the disease are marked. After the 

 second day the treatment cannot be relied upon. The 

 dose necessary was 20 c.cm. of a serum having a potency 

 of i : 10. If too little serum was given, the course of 

 the disease was slowed, the animal improved for a time 

 and then suffered a relapse, and died in from thirteen to 

 seventeen days. The serum also produced immunity, 



