670 



COLLECTED STUDIES IN IMMUNITY. 



the following manner: the original mixture injected subcutaneously 

 is not yet completely neutralized and becomes so only through the 

 catalytic action of the subcutaneous tissues. It is conceivable that 

 this catalytic action might become less with decreasing concentra- 

 tion of the toxin-antitoxin mixture, so that the original concentrated 

 solution proved non-poisonous while a fractional part of the same, 

 through the absence of the neutralizing catalytic action, would still 

 be toxic. Such an assumption would at least explain certain of the 

 observed facts. It seemed advisable, therefore, to repeat the ex- 

 periments in such a way as to exclude the catalytic action of the 

 subcutaneous tissue and this was easily possible by injecting rabbits 

 intravenously. The determinations of the I/ dose for rabbits are 

 shown in the following table: 



TABLE V. 



Having obtained these data, we injected two series of rabbits with 

 dilutions of the following mixtures: 



(a) 0.5 toxin plus 0.004 antitoxin standing 3 hours. 



(6) 0.5 toxin plus 0.003 antitoxin standing 24 hours. 



The result of the experiment is shown in Table VI. 



From this table we see at once that even when intravenous injec- 

 tions are employed, the increased toxicity of fractional portions of 

 toxin-antitoxin mixtures is still strikingly manifested. We shall, 

 therefore, have to assume that really neutralized mixtures of toxin 

 and antitoxin become more toxic on dilution, that, in other words, 

 there is a dissociation of the toxin-antitoxin combination when the 

 mixtures are diluted. From Table VI6, moreover, we learn that 

 this dissociability almost disappears when the mixtures have stood 



