RESUMO
Histologic examinations were made of tuberculin-reaction lesions in four patients with leprosy. The specimens from two of these patients showed the typical "isopathic phenomenon" described by Sagher and coworkers. The histologic picture was leproma-like, with nodules of foamy cells. In the other two cases the tissue reaction to tuberculin was noncharacteristic, although a BCG-vaccination lesion from one of them showed a few foamy-cell nests. The isopathic phenomenon in leprosy appears to be due to a peculiar change in the reactivity of the tissue. This acquired reactivity of the skin may be present many years after leprosy has "burned out". An attempt was made to induce the isopathic reaction in my own skin by adding a suspension of skin from one of the leprosy patients to tuberculin and injecting the mixture intracutaneously. Passive transfer of the isopathic ability did not occur. Apparently the isopathic reaction depends upon the living cells and is not due to a humoral factor, at least not a heatstable one.
