THE PRODUCTION OF ACTIVE IMMUNITY 141 



From this we see that it is possible to establish a certain 

 amount of tolerance by means of daily injections of the 

 poisonous portion. Here again we find that it is compara- 

 tively easy to reach a dose which corresponds to about 

 twice the fatal amount, but above this the animal cannot 

 be carried. When death does result from a dose of the 

 poison which is too large to be borne by the treated pig, the 

 symptoms are identical in all respects with those which 

 occur in the case of an untreated animal, and a fatal result 

 follows in the same length of time. 



The question now arose as to whether these animals 

 which had acquired a tolerance for the poisonous portion of 

 the colon bacillus were more resistant to inoculation with 

 the living germ than were untreated animals. In order to 

 ascertain this point, guinea-pigs which had received from 

 174 to 235 mg. of the toxic portion were inoculated intra- 

 peritoneally with doses of the living germ with the following 

 results : 



TABLE X 



1 c.c. OF A 16-HOUR CULTURE OF THE COLON BACILLUS USED IN THESE 



EXPERIMENTS INVARIABLY KILLED A CONTROL WITHIN 



TWENTY-FOUR HOURS. 



That an active immunity to the living colon bacillus is 

 also developed in rabbits which have been treated with 

 repeated injections of the toxic portion is illustrated by the 

 following experiments: 



