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A genetic investigation has been made to find evidence for a single major gene controlling the reaction of mice to histamine after sensitization with pertussis vaccine. Two inbred mouse strains were chosen: A2G/Lac, which is very insensitive, and C57BR/cd, which is very sensitive. Mice of these strains, and of their F1, F2 and reciprocal backcross progenies, were used to elucidate the genetic segregation. The method depends on the selective sensitivity of the F1 mice to the dilution of the sensitizing vaccine. The results point towards the control of reactivity to histamine by a single major locus, and to a loose association of non-sensitivity with the albino gene. A method is outlined for testing that this association is due to linkage in group I. A comparison is made between this reaction and the anaphylactoid reaction in rats, and suggestions are made for its use in the furtherance of the understanding of allergy and anaphylaxis.

The intracerebral invasion in mice by two Haemophilus (Bordetella) pertussis strains, a virulent strain and the strain 18-323 which is very virulent on intracerebral injection, was studied. The LD 50 of these strains differed by about a thousand times and the average slopes of the regression lines from which these were calculated differed significantly, (P=0.04 and P = O . O l ) . It was found that the number of organisms/mouse brain in infected animaIs reached a maximum count which was slightly higher for the more virulent strain, The day on which the maximum count was reached depended both on the dose of organisms and the strain used, but occurred always before the seventh day after injection. Further, a slightly lower maximum count was reached as the dose of organisms was decreased. The passive protection by rabbit sera, described as antibacterial and antitoxic sera, against both these strains of pertussis organisms, was studied. It was shown that the protection of neither type of serum was due only to the presence of agglutinin antibodies.