Studies on Immunization Against Plague

Plague toxin obtained from autolysates of avirulent P. pestis by fractionation with ammonium sulfate is highly toxic for mice and rats, but almost atoxic for guinea pigs, rabbits and monkeys. The toxin acts mainly on the peripheral vascular system and on the liver, causing haemoconcentration and shock. On local administration, oedema, often followed by tissue necrosis, is marked. There is no physiologic or pathologic evidence that the toxin acts selectively on the central nervous system and on the heart. The shock resulting after injection of a lethal dose of toxin is irreversible and cannot be markedly influenced by drugs or by administration of homologous plasma. The pathologic findings in mice and rats infected with virulent plague bacilli resemble closely those alter injection of the toxin. In other animals no correlation exists between the symptoms and pathologic findings after infection and those after administration of toxin.