Abstract
(1) Fourteen specimens of the sites of the Mitsuda reaction of the seven lepromatous cases which had become posive with chaulmoogra oil treatment were removed from 3 hours to 82 days after the injection and were studied histopathologically.
(2) The nonspecific acute exsudative inflammation with marked infiltration of neutrophile leucocytes and histiocytes was observed until 48 hours after injection, but it disappeared gradually thereafter.
(3) The tuberculoid granulome appears 8-14 days after injection, and this tuberculoid change is regarded as the histological manifestation of positive Mitsuda reaction.
(4) The caseation was not found in the tuberculoid granulome with some exception.
(5) The injected bacilli in the tissue were found even after 82 days.
(6) It is considered as the evidence of getting resistance to lepra bacilli that the subsided lepromatous case, which formaly was negative, give positive Mitsuda reaction.
