IMMUNIZATION OF GUINEA PIGS. 



249 



taken from an 18-hour culture made directly from an infected 

 guinea pig and inoculated subcutaneously. 



Table II. 



Num- 

 ber 

 inocu- 

 lated. 



Previous treatment. 



Died of 

 plague. 



Recov- 

 ered. 



Average 



number of 

 days of 

 survival 

 after in- 

 oculation: 

 fatal 

 cases. 



Remarks. 



8 



7 

 5 

 2 



1 

 3 



2 



5 



Highly immunized survivors of 

 test dose. Table I. 







7 



1 

 2 

 1 

 2 







3 



8 





 4 

 

 



1 



2 

 2 





Slight local infiltration. 



5.4 

 11.0 

 4.5 

 7.0 

 6.5 



Avirulent pest alone. 1 slope 



Avirulent pest alone. J slope 



Avirulent pest alone, i slope 



Avirulent pest 1 slope in 5 to 6i 



cc. ordinary agar. 

 Aviruleht pest i slope in 5 cc. or- 

 dinary agar. 

 Avirulent pest i\ slope in 5 cc. 

 ordinary agar. 



6.3 



In Table II it is seen that of this group all highly immunized 

 animals survived with but little reaction, all nonimmunized 

 controls died, and of the 8 receiving avirulent pest alone and 

 of the 10 receiving agar and avirulent pest one-half survived 

 in each group. The results of this series were somewhat less 

 favorable than that done with the smaller doses. 



Summarizing the results of the two groups, it is seen that the 

 proportion of recoveries following an immunization with this 

 strain of avirulent plague mixed with agar (one-third in group 

 1 and one-half in group 2) is rather less than the proportion 

 obtained by Strong with avirulent pest alone. In the series 

 described here the number of controls which received avirulent 

 pest alone was too few and the doses, for the most part, too small 

 to give a fair comparison. These series were at first intended 

 to serve only as preliminary ones, but the results did not seem 

 favorable enough to warrant a further series with this strain of 

 avirulent plague. The relative inefficacy of this method is shown 

 especially by 3 animals inoculated subcutaneously with agar and 

 avirulent plague. These three showed avirulent plague at the 

 point of inoculation in pure culture twenty-five days after inocu- 

 lation, yet 2 of the 3 succumbed to the test dose of three-fourths 

 million virulent plague. 



As regard the relative immunizing power of single small initial 

 doses of avirulent plague in agar compared with much larger 



