110 INFECTION AND RESISTANCE 



III. Antitoxin unit -f .14 c. c. toxin = no reaction. 



Antitoxin unit -j- .15 c. c. toxin = no reaction. 



Antitoxin unit + .16 c. c. toxin = slight congestion about point of injec- 

 tion, scarcely visible. 



Antitoxin unit + .17 c. c. toxin = apparent reaction at site. 



Antitoxin unit -j- .18 c. c. toxin = edema at site. 

 Lo = .16." 



In determining these values with a large number of toxins Ehr- 

 lich discovered the curious fact that, although there was a rapid and 

 extensive diminution of toxicity in every toxic filtrate in the course 

 of time, there was no corresponding alteration in the L amount. 

 In other words, although more and more of the toxic broth was 

 necessary to kill a guinea pig of standard weight in the required 

 time, the amount of the same broth which neutralized one antitoxin 

 unit remained approximately the same. 12 



In seeking an explanation for this apparent paradox, Ehrlich 

 concluded that we must assume that the toxin is complexly con- 

 structed, consisting of a toxophore and a haptophore group. Assum- 

 ing that chemical union between the toxin and the antitoxin (or, in 

 disease, the body cell) takes place, it is by means of the haptophore 

 group that such union is brought about. The toxophore group, how- 

 ever, is the element by which toxic action is exerted after union 

 by the haptophore group has been accomplished. It would be 

 conceivable, therefore, that in deteriorating in toxicity the toxin 

 might undergo alterations in the toxophore group only, its hapto- 

 phore group, and, therefore, its antitoxin neutralizing properties 

 remaining intact. Such modified toxins, modified only as to the 

 toxophore groups, Ehrlich now refers to as "toxoids." 



In the production of diphtheria toxins for practical purposes it 

 has been found advisable to allow them to "season," that is to stand 

 for prolonged periods until they have reached a state of "equili- 



"II and III are taken from the article by Rosenau, P. H. & M. H. S., 

 Hyg. Lab. Bulletin, 21, 1905. 



12 This statement plainly contradicts the definition of a toxin unit; i. e., 

 the amount which neutralizes 100 toxin units and often leads to confusion 

 among students or others who are unfamiliar with this subject. It should 

 be borne in mind that, while the definition of an antitoxin unit is the one 

 accepted when Ehrlich first arbitrarily established it, the antitoxin unit, 

 as at present in use, is really an amount of antitoxin standardized against 

 L+ quantities of toxin, this last value again obtained by measurement 

 against the original unit. It represents a neutralization value equal to the 

 original one, but may protect the guinea pig against 85, 110, 130, etc. 

 (variable) toxin units, according to the constitution of the particular toxic 

 filtrate employed in the experiment. Indeed, if, in the following pages, the 

 reasoning of Ehrlich is consistently adhered to, our definition of an anti- 

 toxin unit should be: The amount of antitoxin which contains 200 binding 

 affinities for toxin. This will become clearer as the following paragraphs 

 are read. 



