One unit of diphtheria antitoxin was defined as the smallest amount of antitoxin required to neutralise ?

Ans. is 'a' i.e., 100 MLD of toxin . Minimum lethal dose (MLD) of the diphtheria toxin is defined as the least amount of the toxin required to kill a guinea pig weighing 250 gm within 96 hours after subcutaneous inoculation. . One unit of antitoxin was defined as the smallest amount of antitoxin required to neutralize 100 MLD of toxin.