THEORIES OF IMMUNITY. 



doses (if the same proportion of serum contain- 

 ing antitoxine were required as just stated this 

 would need fifty-five cubic centimeters of serum, 

 and an average guinea-pig does not hold so 

 much blood); but where is it possible for the 

 extra antitoxine units to come from? The con- 

 clusion is forced upon us that resistance to a 

 toxine is not necessarily related to the possession 

 of antitoxic power in the serum, but if we are 

 forced to this conclusion, what becomes of the 

 whole theory? In the experiments spoken of 

 above (Ritchie, I. c), the animals could certainly 

 resist sixty-six minimal lethal doses without the 

 slightest symptoms of tetanus, and no part of 

 Ehrlich's theory is as yet capable of giving an 

 explanation of how the toxophorous groups of 

 this amount of toxine are prevented from acting. 



Further, in the later stages of Active Immu- 

 nity — to secure a " strong antitoxine " — thou- 

 sands of minimal lethal doses are injected. In 

 accordance with Ehrlich's theory, the toxine 

 must combine with the tissue cell in order to 

 stimulate the cell to the production of fresh atom 

 groups (H groups, which shall exist in the 



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