INTERREACTIONS OF TOXIN AND ANTITOXIN 77 



referred to several times already, but not fully discussed in order 

 not to interrupt the main line of the argument. 



L has been denned as the amount of toxic solution which is 

 exactly neutralized by i IU of antitoxin, and L + is the amount 

 which, when added to i IU of antitoxin has i lethal dose left un- 

 neutralized. Now if the toxic solution contained a simple sub- 

 stance, we should expect the two quantities to have the following 

 relation in the simple standard toxin of which i c.c. contains 100 

 lethal doses. 



i c.c. toxin(= 100 lethal doses) + i c.c. antitoxin (= i IU) = L . 

 roi c.c. toxin(= 101 lethal doses) + i c.c. antitoxin ( = i IU) = L + . 

 .-. L + -L = o-oi c.c. = i lethal dose. 



This, however, is not the case. If we take a neutral mixture of 

 toxin and antitoxin e.g., of 100 units of the former and i of the 

 latter add to it i lethal dose of toxin, and inject it into an animal, 

 it will not cause death ; there may be transient local cedema and 

 late paralysis, symptoms which are indicative of the presence of 

 free toxon. We must in general add very much more than 

 i lethal dose to the neutral mixture in order to bring about a fatal 

 result. For example, in our standard toxin it might happen that 

 the L + dose was about 1-35 c.c. In other words 



i -oo c.c. toxin solution + i unit of antitoxin = L . 

 I *35 c.c. toxin solution + i unit of antitoxin = L + . 

 L + -L = o-35 c.c. 



This result can readily be explained on Ehrlich's assumption 

 of the existence of substances of differing combining powers for 

 antitoxin. For the sake of simplicity, we will take his earlier 

 nomenclature, and consider the substance as made up of proto- 

 toxoid (with a greater affinity for antitoxin than true toxin has), 

 toxin, and epitoxoid, with little affinity, and corresponding to 

 toxon. The spectrum of the toxin under discussion is : 



150 200 



FIG. 14. 



In this diagram we represent the L dose i.e., i c.c. divided 

 into its component parts. The oblique shading represents, as 



