PREVENTIVE INOCULATION. 445 



use. The preventive fluid thus contains both the dead bodies 

 of the bacilli and any toxins which may be in solution. It is 

 administered by subcutaneous injection, the dose, which varies 

 .according to the "strength," being on an average about 7.5 c.c. 

 Usually only one injection is made, sometimes two ; though the 

 latter procedure does not appear to have any advantage. The 

 method has been systematically tested by inoculating a certain 

 proportion of the inhabitants of districts exposed to infection, 

 leaving others uninoculated, and then observing the proportion 

 of cases of disease and the mortality amongst the two classes. 

 The results of inoculation, as attested by the Indian Commission, 

 have been distinctly satisfactory. For although absolute protec- 

 tion is not afforded by inoculation, both the proportion of cases 

 of plague and the percentage mortality amongst these cases 

 have been considerably smaller in the inoculated as compared 

 with the uninoculated. Protection is not established till some 

 days after inoculation, and probably lasts for a considerable 

 number of weeks. The Commission recommend, however, the 

 employment of a better method of standardisation (this being 

 roughly effected according to the amount of suspended matter 

 present), and also more efficient methods for ensuring the free- 

 dom of the fluid from contaminating organisms improvements 

 which will no doubt be carried out. 



2. Anti-plague Sera. Of these two have been used as thera- 

 peutic agents, viz., that of Yersin and that of Lustig. Yersin's 

 serum is prepared by injections of increasing doses of plague 

 bacilli into the horse. In the early stages of immunisation dead 

 bacilli are injected subcutaneously, thereafter into the veins, 

 and, finally, living bacilli are injected intravenously. After a 

 suitable time blood is drawn off and the serum is preserved in the 

 usual way. Of this serum 10-20 c.c. are used, and injections are 

 usually repeated on subsequent days. Lustig's serum is pre- 

 pared by injecting a horse with repeated and increasing doses of 

 a substance derived from the bodies of plague bacilli, probably 

 in great part nucleo-proteid. Masses of growth are obtained 

 from the surface of agar cultures, and are broken up and dis- 

 solved in a i per cent solution of caustic potash. The solution 

 is then made slightly acid by hydrochloric acid, when a bulky 

 precipitate forms ; this is collected on a filter and dried. For use 

 a weighed amount is dissolved in a weak solution of carbonate 



