TOXIN AND ANTITOXIN 115 



by the "toxin," as measurable upon guinea pigs, a certain fraction 

 of antitoxin being united to toxoid or toxon. It is likely, therefore, 

 as Ehrlich reasoned, that, being higher than 100, and in an ob- 

 viously impure condition approaching but never reaching 200, the 

 valency of antitoxin for toxin was just 200. The correctness of this 

 surmise seemed rendered more probable by Ehrlich's further studies, 

 since analysis of the ingredients of various toxic filtrates, that is, the 

 determination of the relative contents of toxin, toxoids, and toxon, 

 appeared to show constantly definite relations to the valency 200. 



The method by which Ehrlich carried out these subsequent stud- 

 ies is spoken of as the method of "Partial Absorption." In prin- 

 ciple it represents a reversal of his earlier methods of measurement. 

 In these he had titrated various amounts of toxin broth against a 

 constant quantity (one unit) of antitoxin, establishing the L+ and 

 L values. In the method of Partial Absorption, on the other hand, 

 he measured varying fractions of an antitoxin unit against a con- 

 stant amount of toxin, employing for this a previously determined 

 L+ and L dose. A measurement carried out in this way is shown 

 in the following tabulation in which, at the same time, there is indi- 

 cated how many valencies each antitoxin fraction represents, on the 

 basis of an assumed total of 200 for each unit. 16 



antix. unit representing valency + L+ = 85 free T units 



.1 antix. unit representing 20 valencies -f L+ = 85 free T units 



.25 antix. unit representing 50 valencies + L+ = 60 free T units 



.8 antix. unit representing 160 valencies 4" L+ = 10 free T units 



.9 antix. unit representing 180 valencies + L+ = 3.5 free T units 



1.0 antix. unit representing 200 valencies + L+ = 1 free T unit 



It is immediately evident in this table, as it would be evident in 

 any other citation of similar measurements, that there is no regu- 

 larity in the progress of neutralization ; or, in other words, that addi- 

 tion of a definite fraction of antitoxin does not remove the arithmet- 

 ically corresponding amount of toxic properties from the L+ dose. 

 The first 0.1 unit of antitoxin in this table has removed no free 

 toxin whatever. The addition of the next 0.15 of an antitoxin unit, 

 representing 30 valencies, has removed f-f or T \ of the total toxicity. 

 Throughout the scale there is not the regular progression of neutral- 

 ization, multiple by multiple, which would be expected if antitoxin 

 could be titrated against a pure toxin. This, according to Ehrlich, is 

 due to the presence of various toxoids which possess varying affinities 

 for the antitoxin molecule. The first 0.1 of a unit added, in this case, 

 does not diminish the toxicity of the mixture because it is bound by 

 "protoxoids" which possess a higher affinity for antitoxin than the 



16 This measurement is taken from one cited by Ehrlich in Deutsche med. 

 Woch., No. 38, 1898, Vol. 24, and is taken literally except for the first value 

 of 1/10 antitoxin unit, which is inserted to illustrate the formation of pro- 

 toxoids. 



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