The administration of para-aminobenzoic acid in adequate dosage to guinea pigs infected with murine typhus generally prevents the development of fever and scrotal reaction but permits the appearance of rickettsiae in the circulating blood and the formation of complement fixing antibodies.
This rickettsemia appears in the para-aminobenzoic acid treated animals at the same time as that observed in untreated infected animals.
Complement fixing antibodies appear in para-aminobenzoic treated animals and untreated infected animals at the same time. The rise in titer during the period of convalescence is also similar in both groups of animals.
Despite the fact that para-aminobenzoic acid treated animals may exhibit no signs of clinical infection, such animals are immune to subsequent challenge with murine typhus rickettsiae.
There are no substances in the blood of normal or murine typhus infected guinea pigs which, when diazotized, give a color reaction similar to that of para-aminobenzoic acid.
Executive Director, Committee on Medical Sciences, Research and Development Board, National Military Establishment, Washington 25, D. C.