In 1936 we recorded the fact that the effects of prolonged treatment with oestrogenic hormones involved the whole endocrine system and were not confined, as was previously believed, to the sex organs (3, 4). In these papers we described the appearance in the adrenals of non-inbred mice, subjected to prolonged oestrinisation, of a process of degeneration which we had never seen to occur spontaneously in our very extensive animal material, either in non-inbred mice at ages varying from birth up to one year of age or in mice in which skin tumours had been induced by tar painting. This phenomenon was confirmed subsequently by Burrows (1), by Lacassagne and Raynaud (8), and by Dobrovolskaïa-Zavadskaïa (6). It acquired an added interest when it was found by us (4) that a process very similar to that induced in mice of mixed strains by oestrogenic hormones develops spontaneously and fairly regularly in the adrenals of mice of a highly inbred strain with a high incidence of spontaneous mammary cancer—strain R III of Dobrovolskaïa-Zavadskaïa. In this strain the brown degeneration develops spontaneously, i.e. without the application of oestrogens, in both the males and females. In both sexes it is already present when the animals are from four to six months old. It has been found invariably in the adrenals of females of this strain bearing mammary carcinoma. As will be shown in this paper, the same phenomenon has been observed in another inbred strain with a high incidence of mammary cancer—the strain Sable (dilute brown).

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