210 INFECTION AND IMMUNITY 



valency of 200 for toxin. It would require, according to this, 200 T 

 or toxin molecules to satisfy the affinities of one antitoxin molecule. 1 



This belief is based upon the following consideration : In determining 

 the L dose, or fully neutralized toxin-antitoxin union, Ehrlich, as well 

 as Madsen, found that the number of T units contained in such a 

 dose was almost regularly a factor of one hundred, recurring again 

 and again as 25, 33, 50, 75, etc. This pointed to-more or less regularity, 

 in the deterioration of toxin into toxoid, and to a more or less regular 

 relation of toxin to toxon. Now, as we have seen before, if we could 

 procure a perfectly pure toxin, the L dose plus one toxin unit would 

 give us the L + dose; that is, one toxin unit in excess of full neutraliza- 

 tion would suffice to kill a guinea-pig of 250 grams in four to five days. 

 Since a perfectly pure toxin, however, has not been obtainable up to the 

 present time, it is clear that the number of pure toxin bonds contained 

 in L + must be less than the actual number of neutralizing units in the 

 combination, a part of the antitoxin being bound by toxon and toxoid. 

 The actual values obtained for the number of T units in L + has 

 never exceeded 200, and has usually been more than 100, the highest 

 value ascertained by Madsen being 160. Given, therefore, a combining 

 v.alue which, being a multiple of one hundred, is often more than one 

 hundred, but in an obviously impure state has never reached 200, it is 

 most likely that 200 represents the actual value sought for. 



Assuming, therefore, upon the foregoing considerations, that the 

 valency of antitoxin for toxin is 200, Ehrlich carries out his experi- 

 ments in the following way: 



Given a toxin, the unit (T) of which is 0.024 c.c., he first deter- 

 mines the L + dose which, tested against the standard antitoxin unit, in 

 this case is 2.05 c.c. But 2.05 c.c. = 85 T. (or 2.05 -4- .024) units. 

 By mixing the L + dose of toxin and antitoxin in such a way that the 

 quantity of antitoxin is gradually increased, while the toxin remains 

 always L + , and determining upon animals the amount of free toxin 

 contained in each mixture, the following table may be constructed: 2 



antitox. unit representing valencies -\-L + = 85 free T units. 



.1 " 20 " +L+ = 85 " " " 



.25 " " " 50 " +L+ =60 " " " 



.8 " " " 160 " + L + = 10 " " " 



.9 " " " 180 " +L+ = 3.5" " " 



1 Ehrlich, " Schlussbetrachtungen," Nothnagel's System. 



2 Example taken from Ehrlich, Deut. med. Woch., 1898. 



