22 IMMUNE SERA 



The Relations Existing between Toxin and Anti- 

 toxin. The exact nature of the toxin-antitoxin 

 reaction has long been the subject of study and has 

 given rise to considerable discussion. For obvious 

 reasons most of the work has been done with 

 diphtheria and tetanus toxins and their antitoxins. 

 In order to give the reader some conception of 

 the diverging views of various authorities we shall 

 devote a few pages to a brief study of ths diphtheria 

 toxin-antitoxin reaction. 



During the earlier years of toxin-antitoxin in- 

 vestigations the filtered or sterilized bouillon, in 

 which the diphtheria bacillus had grown and pro- 

 duced its " toxin," was supposed to require for 

 its neutralization an amount of antitoxin directly 

 proportional to its toxicity as tested in guinea pigs. 

 Thus, if from one bouillon culture ten fatal doses 

 of " toxin" were required to neutralize a certain 

 quantity of antitoxin, it was believed that ten 

 fatal doses from every culture, without regard to 

 ths way in which it had been produced or preserved, 

 would also neutralize the same amount of antitoxin. 

 Upon this belief was founded the Behring-Ehrlich 

 definition of an antitoxin unit. 1 



The results of tests by different experimenters 

 of the same antitoxic serum, but with different diph- 



1 This unit was " ten times the amount of antitoxic serum 

 necessary to just protect a 250 gramme guinea pig against 

 ten fatal doses of the toxin " 



