THE PRODUCTION OF ACTIVE IMMUNITY 145 



The solution of the residue thus obtained after sufficient 

 extraction with alkaline alcohol is non-toxic in the ordinary 

 sense of the term. However, the toxicity of a substance 

 for the body as a whole depends largely upon whether the 

 cells which it attacks are of fundamental importance in 

 maintaining the life of the animal or not. Thus a poison 

 which possesses a special affinity for the cells of the respira- 

 tory centre will inevitably lead to the production of marked 

 symptoms of poisoning on the part of the animal, while 

 one which exerts its effect upon the blood or connective- 

 tissue cells would not necessarily do so. Of course, in the 

 latter case, treatment over a prolonged period of time would 

 undoubtedly result in symptoms of chronic poisoning. 

 The residue is as potent a cell poison as is the toxic portion, 

 but the cells which it poisons are not directly concerned in 

 the carrying on of a function, the cessation of which would 

 prove immediately fatal to the organism as a whole. That 

 the residue is possessed of but slight toxicity is seen from 

 the fact that the injection of from 300 to 400 mg. into the 

 peritoneal cavity of guinea-pigs at a single dose has appar- 

 ently no effect upon the animal. There is no fall of tem- 

 perature such as is observed after the injection of the 

 poisonous portion, nor, on the other hand, is there any 

 appreciable rise. It may be well to emphasize at this point 

 that in order to study this portion of the colon bacillus and 

 its action it is absolutely essential that the toxic portion 

 should have been completely removed. In order to accom- 

 plish this it is necessary to extract the bacterial cell sub- 

 stance at least three times with the alkaline alcohol, and 

 frequently a fourth extraction is required. If all of the 

 poisonous portion has not been removed, the treated animal 

 begins to show evidences of poisoning, as lowering of tem- 

 perature, stupor, and, provided the extraction has been 

 very imperfect, death. These symptoms do not, however, 

 become manifest to a marked degree until from two to 

 four hours after the injection. This is in marked contrast 

 to the rapidity with which the free poison acts, and would 

 indicate that the poison in the imperfectly extracted residue 

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