A study of the properties of sera obtained by immunization of rabbits with fractions of the plague bacillus

Experiments were carried out on white mice. Sera were obtained from rabbits immunized with 1B and II fractions ofP.pestis, and with the water-insoluble residue of the EV strain; only the latter serum possessed therapeutic and protective properties. Normal serum, and sera from rabbits immunized with the two other antigens showed no differences with respect to these properties. The sera of rabbits treated with the EV strain did not differ significantly from the sera of others immunized with fractions 1B and II ofP.pestis with respect to the power to neutralize toxin.