The preparation of any standardized antitoxic serum of a reliable concentration depends on the possibility of measuring the antitoxic content of the serum in terms of its power to prevent specifically a biologic reaction to a definite amount of toxin. The lack of such a specific biologic phenomenon for the detection and measurement of the toxins derived, for instance from Bacillus typhosus, Meningococcus, Bacillus coli and Pfeiffer's bacillus, has served to delay the preparation of therapeutic serums of uniform potency. With serums such as the antimeningococcic serum, which are presumed to owe their therapeutic value to the presence of bactericidal properties, the possibility exists that the presence of undetermined amounts of antitoxin may explain the generally recognized variability in therapeutic efficacy.1
The discovery by one of us (G. S.2) of the phenomenon of local cutaneous reactivity to bacterial filtrates has offered a new biologic reaction by means of