PROTECTIVE INOCULATION. 



239 



are that 70 per cent of these animals appeared to be immune 

 against plague infection entering through the mucous mem- 

 branes of the mouth and throat, but one can not conclude that 

 this same percentage of animals would have proved to be im- 

 mune if the organism really had been introduced directly into 

 the lung by the bronchi. 



Let us consider the experiments in relation to monkeys which 

 give us much clearer information regarding immunization 

 against pneumonic plague. Three series of experiments were 

 performed as follows: 



EXPERIMENT NO. 3. 



Eleven * monkeys were vaccinated on June 23, 1911, each with one 48- 

 hour agar-culture of avirulent plague. They were subjected to infection 

 by inhalation as follows: Two vaccinated monkeys with two controls on 

 July 7; 5 vaccinated ones with 5 controls on July 12; 5 vaccinated ones 

 with 6 controls on July 14. The general mode of procedure was the same 

 as in the preceding experiments. The result was as follows: 



- Series III. — Infection by inhalation. 



Vaccinated monkeys. » 



Normal monkeys. •> 



No. 5404 died in 5 days. 



No. 5437 died in 4 days. 



No. 5386 died in 5 days. 



No. 5438 died in 4 days. 



No. 5384 died in 6 days. 



No. 5439 died in 5 days. 



No. 5394 died in 5 days. 



No. 5440 died in 5 days. 



No. 5393 died in 5 days. 



No. 5501 died in 5 days. 



No. 5400 died in 4 days. 



No. 5424 died in 3 days. 



No. 5401 survived. 



No. 5425 died in 3 days. 



No. 5387 died in 3 days. 



No. 5491 died in 4 days. 



No. 5389 died in 5 days. 



No. 5492 died in 3 days. 



No. 5403 died in 5 days. 



No. 5493 died in 4 days. 



No. 5390 died in 4 days. 



No. 5494 died in 3 days. 





No. 5495 died in 3 days. 



» Total : Survived, 1 ; died, 10. 

 " Total : Survived, ; died, 12. 



Only one of the vaccinated monkeys, or 9 per cent, survived, 

 while all of the controls died of pneumonic infection. 



EXPERIMENT NO. 4. 



On September 15, 1911, twenty-two monkeys were vaccinated each with 

 one 48-hour agar-culture of living avirulent plague bacilli. Two weeks 

 later they, together with 22 unvaccinated monkeys, were subjected to 



* Additional monkeys were vaccinated in this and the following series 

 but died in a cachectic condition before the date for testing their immunity 

 arrived. In no instance were we able to show that they died of plague. 



