TOXIN AND ANTITOXIN 107 



ization was accelerated by moderate heat and by concentration of the 

 reagents and, most important of all, that the reaction followed 

 roughly the law of multiple proportions, characteristics, all of them, 

 which were entirely analogous to chemical reactions in general. 

 When he added 0.3, 0.5, 0.75, 0.1, etc., cubic centimeters of serum 

 from a ricin-immune goat to constant quantities of ricin, and then 

 added rabbit cells, the hemagglutinating properties of the ricin were 

 inhibited in direct proportion to the amount of antiricin mixed with 

 it. And his test tube experiments were further found to represent 

 with much accuracy the occurrences which took place within the 

 animal body. For, similar mixtures injected into mice were toxic 

 in direct proportion to the balance of ricin and antiricin established 

 in the injected material. 



Although the views of Ehrlich and his followers have great im- 

 portance in connection with the union of antigens and their anti- 

 bodies in general, these ideas were worked out by him most elab- 

 orately in connection with his efforts to arrive at a practicable and 

 accurate method of establishing a standard of strength for diphtheria 

 antitoxin, and it is essential that we consider this work in detail. 



The earlier attempts to standardize diphtheria antitoxin by the 

 use of living cultures (Roux and Behring) were soon abandoned, 

 since it was found that the accurate establishment of fixed lethal 

 doses of the culture was not possible. When the facts, just recorded, 

 concerning the interaction and quantitative relations of the soluble 

 toxins and their respective antitoxins came to light, Behring intro- 

 duced the standardization of the curative sera by the use of toxins, 

 both in the case of tetanus and in that of diphtheria. In order to 

 do this consistently he established for diphtheria poison an arbi- 

 trary toxin unit which he defined as the amount of any given diph- 

 theria filtrate sufficient to cause death in a guinea pig of 250 

 grams, and, borrowing the terms from chemical nomenclature, he 

 designated as a "normal" diphtheria poison one which contained 

 100 such units in one cubic centimeter. (D T !N", M2 50 = diph- 

 theria toxin normal, Meerschweinchen 250 grams.) 



Together with Ehrlich, Behring then established an antitoxin 

 unit (I-E, Immunitats Einheit). They designated as a "normal" 

 antitoxic serum one "which contained in one cubic centimeter one 

 antitoxic unit" (I-E), and state further, "of this serum 0.1 c. c. 

 neutralizes 1 c. c. of the Behring normal toxin." (Conf. Madsen in 

 "Kraus u. Levaditi Handbuch," II, p. 94.) Alterations were subse- 

 quently made in this scale of standards and Ehrlich later desig- 

 nated as an antitoxin unit a quantity of an antitoxin which 

 completely neutralized 100 lethal doses (for guinea pigs of 

 250 grams) of a poison at that time in his possession. The unit 

 of diphtheria antitoxin at present in use therefore may be defined as 

 a quantity of serum sufficient to protect a guinea pig of 250 grams 



