THEORIES OF IMMUNITY. 



through the blood, the II group of the tissue 

 cells overcomes the attraction of the H group 

 in the antitoxine, and binds the toxine to itself, 

 so that the irritant action of the toxine may 

 occur. This, however, is no explanation, for it 

 supposes exactly the opposite of what was sup- 

 posed in the previous clause: in the present 

 instance, that the H groups of the tissue cells 

 have a stronger affinity for the H groups in the 

 toxine than have the H groups of the antitoxine, 

 while in the preceding paragraph the opposite 

 supposition is made to explain what is seen in 

 diphtheria immunity. 



Another very perplexing question is brought 

 forward in the same place : What is it that pro- 

 duces the safety of the animal in the very early 

 days of the process of immunity against a toxine? 

 Active immunity? In experiments quoted by 

 Ritchie (I. c), and upon tetanus toxine, it was 

 shown that 0.5 gram of antitoxic serum was 

 sufficient to neutralize one minimal lethal dose 

 of the tetanus toxine; as a matter of fact, the 

 animals resisted in the series spoken of an 

 average of one hundred and ten minimal lethal 



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