PROTECTIVE INOCULATION. 243 



In conclusion, our experiments have demonstrated that vac- 

 cination does not afl'ord the same protection against pneumonic 

 plague that it does against bubonic plague in experimental 

 animals. They indicate strongly that prophylactic inoculation 

 can not be relied upon as even a reasonable means of protection 

 against pneumonic infection in man. It would appear that a 

 proper mask furnishes the only reliable method of protection. 



