234 STRONG AND TEAGUE. 



Table I. — Combined table comparing efficiency, etc. — Continued. 



NATURAL AGGRESSIN. 



Kind of animal and series No. 



Number 



inoc- 

 ulated. 



Number 

 dead 



before 

 immunity 



tested. 



f 

 Immunized. 



1 



Number. 



Percent- 

 age. 



Guinea pigs: 



Series 35 



15 

 12 





4 

 4 



26 

 33J 







Total 





27 





8 



30 







KLEIN'S METHOD. 



Guinea pigs: 



6 



7 





2 

 2 



83i 

 28 



Series 56 - .. - 





Total 





13 





2 



30 







It is demonstrated that in the case of guinea pigs, vaccinated 

 with an avirulent culture, about 80 per cent are protected against 

 a severe cutaneous plague infection, and in monkeys, vaccinated 

 in the same way, about 61 per cent are so protected against sub- 

 cutaneous infection. 



It was possible to immunize against the same severe cutaneous 

 test but 26 per cent of the guinea pigs with killed cultures. 

 Kolle and Otto, in numerous previous experiments on guinea 

 pigs, were never able to immunize more than 10 per cent of 

 these animals by means of repeated inoculations of killed cultures. 

 It will be noted also in the accompanying table that in the 

 experiments in which living attenuated cultures were used for 

 the immunization of guinea pigs, in one series 72 per cent and 

 in another 88 per cent were protected against cutaneous infec- 

 tion. These experiments are confirmatory of the statement 

 that the living attenuated culture gives a much higher degree of 

 immunity against cutaneous plague infection than a killed one. 



In order to retest the value for immunization against cutaneous 

 infection of the culture used for the vaccination in the experi- 

 ments recorded in this paper, the following experiment was 

 performed : 



EXPERIMENT NO. 1. 



Twenty-four guinea pigs each received subcutaneously on June 9, 1911, 

 one 48-hour agar-slant-culture of living avirulent plague. One died (in- 

 traperitoneal inoculation) in less than twenty-four hours after vaccination 

 and the others survived. Two weeks later, 11 of these vaccinated guinea 

 pigs were subjected to infection with virulent plague bacilli by cutaneous 



