On the antigenicity of diphtheria toxoid. IV. The usefulness of the quantitative Schick test as the response in the assay of immunizing potency.

Several diphtheria toxoid preparations were fractionated by salting out with ammonium sulphate at various concentrations into several fractions possessing evidently different immunizing potency. The fractions of lower solubility were proved to possess less potency than those of higher solubility when the comparison was performed at the same Lf dose6). This difference between the potency of these fractions seems not to be due to the presence of certain synergistic or antagonistic active substances in the medium, in which the toxoid was contained6, 10). Ishizaka et al.4) reported using Schultz-Dale's procedure, that no difference was observed between these fractions in the time lapse necessary for the initial combination with diphtheria antitoxin in spite of the distinct difference observable in the time lapse necessary for the appearance of flocculation. The capacity of producing allergic reactions such as Arthus reaction and anaphylactic shock in guinea pig, previously sensitized with several kinds of diphtheria toxoid fraction, was found to be parallel to the Lf value, but not to the immunizing potency7). In view of the above, the experiments were performed in an attempt to find out as to whether the specific active principle contained in these fractions has identical quality in respect to immunogenicity and whether the immunizing potency of diphtheria toxoid preparations can be expressed in terms of the unit refering to the standard preparation. Part of the results thus obtained was described in our separate papers8), in which the similarity of the effective constituent of the toxoid preparations was chiefly analysed by means of circulating antitoxin titre alone as the response, and no deviations from parallelism of the dose-antitoxin response regression lines of the diphtheria toxoid fractions was found, which possess various grades of solubilty and which was showing striking differences in immunizing potency in vivo. Thus Wood's •gHypothesis of Similarity•h or Finney's •gCondition II•h1,5) was not disproved. In this experiment, the quantitative Schick test2) was carried out simultane-