To establish a quantitative method for titration of the heatlabile toxin of Bordetella pertussis by the skin reaction, various conditions were examined and their relative merits assessed.
The skin reaction of the rabbit was characterized by a pale, ischemia-like spot with or without petechial hemorrhage, while hemorrhage was prominent in the guinea pig and suckling mouse. Mean diameters of the pale spot in the rabbit and of the hemorrhagic spot in the other species provided a linear regression on log dose over a relatively wide range. The regression co-efflcient was not affected by endotoxin or the lymphocytosis-promoting factor, though endotoxin intensified the reaction in the guinea pig and suckling mouse. These facts enabled us to construct a statistically valid assay method. Animal variations were controled by expressing the toxicity relative to that of a reference.
An absolute unit of the toxicity was defined. Normalization of toxicities determined under different conditions is possible.