The Antirachitic Activity of Monochromatic and Regional Ultraviolet Radiations.

Abstract

In a communication published some years ago it was shown that ultra-violet rays longer than about 324μμ exert no antirachitic potency, and that waves 302μμ are of great value in this respect. Somewhat later we suggested, as the results of experiments with selective filters, “that the intense line of the mercury vapor spectrum 302μμ in length conferred definite protection and that the 313μμ waves exerted probably a feeble action in this respect.” The question as to whether antirachitic potency ceases at the 313μμ or the 302μμ level is of both theoretical and clinical importance, as the shorter rays are present to but a small extent and in low intensity in the solar radiations which reach the surface of the earth. This is especially the case where the rays are intercepted by moisture or smoke. It, therefore, seemed worth while to make a more minute dissection of the spectrum in this region. This has been accomplished by means of the isolation of these two lines of the mercury vapor spectrum and testing their power to activate cholesterol. The radiations were of equal intensity, and the same amounts (2.5 mg. per capita daily) of the irradiated cholesterol were fed to rats which had been rendered rachitic. Without going into detail at this time, it may be stated that a series of experiments of this nature showed that the 302μμ line possessed marked antirachitic potency, whereas the 313μμ line exerted very slight specific power. This result emphasizes more strongly than ever the remarkable specificity of wave lengths of light in relation to rickets. It has never been accurately determined whether radiations less than 290μμ, the shortest emitted by the sun, have curative power in rickets.