Experimental Production of Malignant Tumors in the Albino Rat by Means of Ultraviolet Rays

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Abstract
Several different lines of investigation within recent years have focused attention upon the metabolic aspects of cancer, a review of which has been published by one of us (1). The brilliant work of the English investigators, Kennaway, Cook, Hieger, and their coworkers (2–5) has established the chemical nature of the carcinogenic hydrocarbons present in tar and their relation to the estrogenic hormones. Reviews of these studies have been published by Dodds (6) and Loeb (7). Recent investigations on the chemical nature of the bile acids, cholesterol, calciferol (one form of vitamin D), male and female sex hormones, cardiac aglucones, and the carcinogenic hydrocarbons have shown them all to contain a condensed carbon ring group of compounds, the skeleton key of which would be phenanthrene. Cook and Haslewood (8) and Wieland and Dane (9) have prepared methylcholanthrene from desoxycholic acid, one of the bile acids. Fieser and Seligman (10) also prepared it from cholic acid, another of the important bile acids. Methylcholanthrene is one of the most active carcinogenic agents known at the present time. Reviews of the chemical and biological effects of ultraviolet rays have been published by Ellis and Wells (11) and Laurens (12, 13). Of all radiations these are by far the most dangerous to the eye. They are invisible and nature does not usually protect the eye from their effects. According to some workers the production of cataract is due, at least partially, to the action of rays of short wavelength. When present in large quantities these have been shown to give rise to a certain turbidity of the lens. Recent work by Clark (14) is interesting in this connection. Extracts of lens proteins were made in solutions of sodium, potassium, and calcium chloride. When the extracts were heated to 40° C. for two hours after ultraviolet irradiation, opacity became marked in those containing calcium, but not in the presence of potassium. The ultraviolet rays caused light denaturation of the lens, which then became opaque in the presence of as little as 0.05 per cent calcium.

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