THEORIES OF IMMUNITY. 



the excess of atom-groups is thrown out from 



the cell and exists free in the blood stream as 



H+X, which is the antitoxine. 



This is not only the simplest way for illus- 

 trating what goes on in passive immunity (the 

 use of diphtheria and tetanus antitoxine), but 

 this passive immunity and the production of the 

 antitoxine is the simplest form of immunity that 

 workers in the subject are called upon to ex- 

 plain. In giving the formulas thus far shown, 

 it is of course to be understood that only the 

 simplest forms are used, and that the X dis- 

 played must be supposed to contain all the other 

 atom-groups that are useful in other reactions, 

 but not in the particular one under discussion. 



The believers in the physiological explana- 

 tion of the condition of immunity are not under 

 the necessity for supposing any such reaction 

 as that just illustrated; they believe that the 

 antitoxine excites the cells to resist the toxine, 

 and the evidence for this rests upon the series 

 of experiments (Buchner, Calmette with snake 

 venom, Wassermann) in which it was appar- 



53 



