202 LECTURES ON IMMUNITY 



agreement between observation and the calculation by 

 which no prototoxoid is supposed to exist, is very good 

 for low values of n. The hypothesis of prototoxoids 

 seems therefore untenable. But on the other hand, the 

 poisonous effects of No. 471 had fallen very remarkably 

 in the seventeen months to very nearly half the original 

 toxicity without change in the antitoxin-binding property 

 of the poison. For this same reason Ehrlich supposed that 

 the poison is slowly converted into an innocuous or less 

 poisonous substance with the same antitoxin-binding prop- 

 erties as the toxin itself (cf . p. 1 84). This new substance 

 is called syntoxoid by Ehrlich. 



The several preparations of diphtheria-toxin differ 

 from each other in showmg rather marked differences 

 in their constants of equilibrium: No. 471, JT=o.oi2; 

 poison A, ^=0.03; poison C, K= 0.004. It will be nec- 

 essary to make new experiments on this interesting ques- 

 tion (and similar ones for tetanolysin) before this can be 

 elucidated. The observed peculiarity, that K has rather 

 different values, might be explained by supposing that the 

 poison is loosely combined with or absorbed by some 

 concomitant substance, for instance by albuminous sub- 

 stances contained in the preparations, and that therefore 

 only a certain fraction of the toxin enters into the equi- 

 librium with antitoxin. This fraction is different in differ- 

 ent preparations of the diphtheria poison, according to 

 their different content of the reacting proteins, and the 

 less this fraction the greater would be the constant of 

 the equilibrium. This view is supported by the observa- 

 tion of Madsen that the value of K for another poison, 

 namely crotalus venom, is different when injected into 



