Wickham and Degrais1 have microscopically determined that "cancer cells, exposed to radium after a primary hypertrophy, disorganize, become soft, disintegrate and are probably eliminated by a phagocytosis. The connective tissue enveloping and separating the mass of cancer-cells, on the other hand, is stimulated and regenerated by the invasion of embryonic nuclei, which dissociate the groups of cancerous cells, finally replacing them. These modifications tend to a fibrous transformation of the tumor, producing, as we know, the unusually good scar that results with such a healing." That any one of the three so-called alpha, beta or gamma rays has an advantage in producing this effect I cannot affirm. I should rather believe that in the method I use the results are probably due to the great amount of rays to which the tissues are exposed, for I use no screen except a thin layer of mica which only filters out