142 PROTEIN POISONS 



Rabbit No. 1 received between May 25 and July 5 eight 

 injections of the toxic part, the total amount of poison 

 injected being 855 mg. On July 8 this animal received 

 5 c.c. of a twenty-four-hour culture of the living germ 

 without apparent effect. The control inoculated at the 

 same time was found dead in eight hours. 



Rabbit No. 2 received between May 28 and July 18 

 eleven injections of the toxic portion, the total amount of 

 poison given being 2475 mg. On July 27 this animal was 

 inoculated with 5 c.c. of a sixteen-hour culture of the colon 

 bacillus without effect. The control was found dead in 

 ten hours. 



Rabbit No. 3 received between June 27 and July 18 seven 

 injections of the poison, the total amount given being 2100 

 mg. On July 28 this animal was inoculated with 6 c.c. of 

 a twenty-four-hour colon culture. Recovered. 



Rabbit No. 4 received the same amount of poison as the 

 preceding one. Twelve days after his last treatment this 

 animal was given 6 c.c. of a forty-hour colon culture and 

 recovered. The control was found dead in eight hours. 



From the foregoing experiments it becomes evident that 

 animals which have been treated with the toxic portion of 

 the colon bacillus acquire a certain degree of immunity to 

 the living germ. We are as yet unable to state whether it 

 is possible to obtain a high degree of immunity with the 

 poisonous portion or not. Thus far we have had animals 

 which have withstood inoculation with from two to four 

 times the fatal dose of the living germ. It is worthy of 

 note in this connection that animals which have received 

 one injection of a non-fatal dose of the poison are able to 

 withstand inoculation with twice the lethal dose of the 

 living germ on the following day. The immunity which 

 follows a single injection is, however, exceedingly transitory, 

 and has usually disappeared on the second day following 

 the treatment. This would seem to be the most marked 

 difference between the immunity which results from a 

 single injection of the toxic part and that which follows a 

 series of injections extending over a considerable interval 



