VACCINES IN PROPHYLAXIS OF DISEASE 215 



at intervals of ten days, and the duration of 

 immunity is about one year. The first dose con- 

 tains 500 million killed bacteria, and the second 

 dose 1,000 million. 



Results Haffkine found a considerable re- 

 duction in the incidence of the disease, but no 

 reduction in mortality among the inoculated 

 persons who became infected. The degree of 

 protection seemed to increase during the first 

 four days and to last about fourteen months. 

 During the Japanese epidemic of 1902 there 

 were 77,907 persons vaccinated. The mortality 

 was reduced from 75 per cent to 42 per cent. In 

 Bilibid prison, Strong inoculated over one-half 

 the inmates, some 1,838 persons, among whom 

 four cases of cholera subsequently appeared. 

 Immunization will in no sense replace sanitary 

 measures in repressing cholera, but apparently 

 it is useful in regions where the disease has al- 

 ready broken out. Since 1896 the Indian Gov- 

 ernment has maintained a regular station for 

 the vaccination of coolies in order to prevent 

 the spread of the disease. 



PLAGUE 



Prevalence The history of bubonic plague 

 can be traced back to the third century. In 



