Abstract
In a previous communication we showed that the development of rickets in rats fed the standard rickets-producing diet of Sherman and Pappenheimer can be prevented by daily exposures to direct sunlight for fifteen minutes. 1 A similar result has been reported by others. 2 If the rats are placed in a box having flint glass windows, it was found that the sun's rays which had traversed the glass had lost their protective power. Rays which were reflected to the rats from a white surface retained some of their efficacy. Rickets can be prevented in rats by daily exposures of about 2 minutes to the rays of the mercury vapor quartz lamp, or by 4 minutes or less exposure, at a distance of three feet, to the rays from a carbon are lamp. X-rays were found ineffective.
In order to test the effect of the pigment of the skin on the protective action of light, a group of white and another group of black rats (the melanic form of the Norway rat) were exposed to the radiation from the mercury lamp. In the first experiment both sets of animals were protected as the dosage was excessive. In the second experiment, when one and one-and-one-half minute exposures were employed, all the white but none of the black rats were protected. The black rats showed rickets by x-ray and by
pathological examination, and their blood contained a less percentage of inorganic phosphate. This experiment shows that pigment retards the rays which are effective in rickets, and indicates one factor in the exceptional susceptibility of negro infants to this disorder.
Prolonged exposure to direct sunlight failed to prevent or to delay the onset of scurvy in giunea-pigs.
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