Experiments on the theory of photochemical formation of carcinogens from skin fats.
Irradiation products of skin surface fats, including digitonin-precipitable sterols, isocholesterols, and total unsaponifiable fractions, were painted on the ears of white mice for periods of from 15 to 18 months, but failed to produce precancerous or cancerous changes that could be noted histologically. Therefore, the theory of photochemical formation of carcinogenic compounds on the surface of the skin by ultraviolet irradiation could not be substantiated by this method.
Studies on the Hypothetical Carcinogenicity of Irradiated Sterols: I. The Effects of Irradiated Cholesterol on the Skin of Mice
In numerous publications Roffo (1) has advanced the conception that actinic or sun cancer is caused by some interaction between the ultraviolet solar rays and the cholesterol present in the skin. The principal points of this hypothesis may be summarized as follows: (1) Cholesterol is a heliotropic substance which migrates to those parts of the skin which are subjected to light. (2) Cholesterol is an “accumulator of actinic energy.” “Under the influence of ultraviolet light and the oxidation which accompanies it, the sterol loses its characteristic chemical reactions and acquires new properties as ionization, fluorescence, luminescence, radiation, and photoactivity.” (3) Cholesterol is photo-oxidized by ultraviolet light in the presence of air. It loses the side chain, undergoes “esterification of the tetracyclic ring system,” and is finally dehydrated to a carcinogen resembling derivatives of the phenanthrene series. The assumption that the action of light is an indirect one, involving changes in some of the constituents of the skin, is an interesting one and may be accepted as the basis of a working hypothesis. Roffo9s theory in regard to the role played by cholesterol in the formation of sun cancer, however, has up to the present time not been substantiated by conclusive physical or chemical evidence.
An Essay on the Nature and Significance of the Normative Nature of Economics
It is conventional in economics to distinguish between the normative and the positive. The normative has to do with goodness and badness, and with what ought and ought not to be done;1 and the positive has to do with objective description and/or explanation, with what is and with what is necessary given some normative end. The normative has to do with desirability; the positive has to do with truth (in the sense of either descriptive accuracy or serviceability of a means to a given end).2