depth is near the base of the hair follicle which comprises the deepest reservoir of epithelial cells of the germinal layer, it was suggestive that this might be a critical region in the observed carcinogenesis. The suggestion gained sianificance from the observations that most of the tumors are Similar to hair follicles, and that in the non-ulcerogenic Gose range the number of tumors per rat was in nearly constant razio (1/2000-1/41900) with the number of atrophied hair Thus the carcinogenesis in this experiment N25 remarkadly correlated with the dose to and specific of a varticular skin structure. When exposures were stripe and sleve patterns of reughly 1 mm scale, geometrical efiects ware observed: moSt nowtadly the cancer inguction in the sieve ceometry was suporessed at doses of cr 1790 rad but not at doses of 2300 rad. The reduction, however, w25 acain consistent with the reduction in Gamage as characterized cnis important experiment, a high incidence cancer was cbserved after intense local doses of radiation, arcinocenesis was proportional to the damage or qr ae ® a w ay Z of ty oO To summa ty by atrophiec hair follicles. 2rtordering of 3 gritical architectural unit of the tissue,