TOXONE REACTION 337 



amount 100 units of antitoxin are added so as to form a 

 physiologically neutral mixture, the combination which 

 occurs is shown by the following " equation " : 90 toxin- 

 antitoxin -f- 10 toxone-antitoxin = L (i.e. neutrality). 

 If an amount of the toxin broth be now added, corre- 

 sponding to 1 1 units of toxin, the effect will be as though 

 only one unit of toxin has been added, as is shown by the 

 following " equation " : 90 toxin-antitoxin +10 toxone- 

 antitoxin -f- 11 toxin 100 toxin-antitoxin + 10 toxone 

 (free) + 1 toxin (free) = L + (i.e. just acutely lethal). 

 Thus although the equivalent of eleven minimal lethal 

 doses of toxin has been added to the physiologically 

 neutral mixture of toxin broth and antitoxin, only one 

 minimal lethal dose of toxin remains free and active, 

 because ten toxin units displace the ten toxone units from 

 the toxone-antitoxin complex and are neutralised by the 

 antitoxin thus set free. Ehrlich, therefore, devised a 

 method of standardisation which eliminates irregularities 

 due to the variable proportions of toxone and toxin in 

 the toxin broth by adopting antitoxin and not toxin 

 as the standard. In order to standardise an antitoxin, 

 a virulent toxin broth is employed and its minimal lethal 

 dose is approximately ascertained i.e. that amount 

 which is just sufficient to kill a 250-grm. guinea-pig on 

 the fourth or fifth day. A solution of accurately stan- 

 dardised antitoxin, formerly obtainable from the Serum- 

 spriifung Institut, Frankfort-on-Maine, is then prepared, 

 containing one " unit " of the antitoxin in 1 c.c., and the 

 toxin is standardised with this by mixing with one unit 

 various quantities above and below one hundred minimal 

 lethal doses. It is required to ascertain the amount 

 of the toxin broth which, when mixed with one unit of 

 antitoxin, just suffices to kill a 250-grm. guinea-pig on 

 the fourth or fifth day after the injection of the mixture ; 

 this amount of toxin is known as the L + dose. The L + 



M.B. 22 



