In a previous paper,1 we recorded the results of a study of the variation of the antirachitic effect of sunshine in Toronto from December, 1926, to June, 1927. The procedure consisted in the daily exposure to sunshine from 11 a. m. to 1 p. m. of albino rats fed on McCollum's rachitogenic diet 3143.2 Control rats fed on the same diet were kept inside. After four weeks, the rats were killed; the amount of phosphorus in the blood was estimated; roentgenograms were taken of the legs, and the percentage of ash in the femora and tibiae was determined. Every Monday, throughout the period of the investigation, this procedure was begun on from twenty-five to forty rats. As a result of the study, we concluded that the sun's rays, in the latitude of Toronto, during December, January and February, produce a slight but definite antirachitic effect on rats fed
TISDALL FF, BROWN A. SEASONAL VARIATION OF THE ANTIRACHITIC EFFECT OF SUNSHINE: II. Am J Dis Child. 1928;36(4):734–739. doi:10.1001/archpedi.1928.01920280085007
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