TOXINS AND ANTITOXINS 259 



bouillon had retained its full original power of neutralizing anti- 

 toxin. If the reaction was purely one of chemical neutralization, 

 there seemed to be but one explanation of this. The toxin molecule 

 must contain two separate atom groups. One of these must possess 

 the power of binding antitoxin and be stable; this he designates 

 as the "haptophore" or "anchoring" group. The other, the one 

 by which the toxin molecule exerts its deleterious action, must be 

 more easily changed or destroyed; this he calls the "toxophore" 

 or "poison" group. In the altered toxin-bouillon in which a part 

 of the poisonous action has been lost while the antitoxin-neutralizing 

 power is intact, the toxophore group of some of the toxin must 

 have been changed or destroyed. Such altered toxin he speaks of 

 as "toxoid." 



In support of this hypothesis and for the purpose of perfecting 

 the methods of standardization, Ehrlich was led to determine, for 

 a large variety of specimens of diphtheria toxin, the precise quan- 

 tity, in cubic centimeters, which was necessary to neutralize exactly 

 one unit of his standard antitoxin. This he accomplished by making 

 a series of toxin-antitoxin mixtures, in each of which the quantity 

 ef antitoxin was exactly one unit, while the amount of toxin was 

 gradually increased. These mixtures were injected into guinea-pigs 

 of 250 grams weight. It is self-evident that in such an experiment 

 the mixtures containing the smaller quantities of toxin would have 

 no effect upon the guinea-pigs. Soon, however, a mixture would be 

 reached in which toxin would be sufficiently in excess of antitoxin 

 to produce the symptoms of slight poisoning, as evidenced in local 

 edema, rise of temperature, etc. The largest quantity of toxin which 

 could be added without producing such symptoms was then regarded 

 as exactly neutralizing the antitoxin unit. This quantity of toxin 

 Ehrlich speaks of as "Limes zero" (Limes = threshold) or, briefly, 



"L ." 



For instance: 



One antitoxin unit -f- 0.6 c.c. toxin ...... No symptoms of poisoning. 



" " " 0.8 c.c ........... " " " " 



" " . " 0.9 c.c ........... " " " " 



u " " 1. c.c. , " " ll " 



1.1 c.c ........... Local edema. Paralysis in 30 days. 



1.2 c.c ........... Death in 10 days. 



In this example, L , therefore, equals 1 c.c. 



