THE PRODUCTION OF ACTIVE IMMUNITY 153 



the injection of the dead culture. In fact, several of them 

 have shown signs of the commencement of the convulsive 

 stage as evidenced by slight convulsive movements of the 

 head separated by considerable intervals of time. We have 

 been unable to secure a fatal result in these animals up to 

 the present time simply because we have worked with pigs 

 which did not possess a sufficient amount of bacteriolytic 

 substance directly available to cause disintegration of 

 enough bacilli to liberate a fatal amount of poison at one 

 time. It is worthy of note that this behavior of animals 

 immunized with the residue toward the dead bacterial sub- 

 stance furnishes additional proof of the fact that the poison 

 of the colon bacillus is an intracellular one. If the poison 

 existed free in the culture medium we should expect that 

 the control would show evidences of its action at as early 

 a period as does the treated animal. However, as has 

 been stated above, this is not the case. The fact that the 

 treated animal show r s symptoms of poisoning to a much 

 greater degree and at an earlier time than does the control 

 can be explained only on the ground that the poison with 

 which we are dealing is an intracellular one and is set free 

 only after the disintegration of the bacillus by bacteriolysis. 

 The question now arose as to whether the immunity 

 induced through the residue is specific for the colon bacillus 

 or not. In order to test this point, animals which had been 

 treated with this portion were inoculated with living cul- 

 tures of the typhoid bacillus with the following results: 



TABLE XII 



1 c.c. OF A 16-HOUR CULTURE OF THIS TYPHOID BACILLUS KILLED 



CONTROLS WITHIN TWENTY-FOUR HOURS. J c.c. 



DID NOT CAUSE DEATH 



