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To the Editor:
—In a recent paper (The Journal, January 21) Macht, Anderson and Bell publish results of measurements which may lead to a false conception concerning the penetration of ultraviolet rays through animal tissues. Two methods are used for the determination of the transmitted radiation, a photographic method with use of a spectograph and a thermopile with use of a monochromator. Although the correctness of the photographic observation cannot be doubted, it seems advisable to estimate the percentage of the radiation transmitted which caused the ultraviolet spectral lines to appear on the plate. The exposures were made by air-cooled and water-cooled mercury arcs at very short distances (from 5 to 8 cm. and 20 cm., respectively) with a very wide slit (about 1 mm.). The time of exposure varied from one-half to five minutes and was from five to ten seconds in two cases (cat, 0.9 mm.; rabbit, 1
Bachem A. THE PENETRATION OF ULTRAVIOLET RAYS INTO ANIMAL TISSUE. JAMA. 1928;90(7):563. doi:10.1001/jama.1928.02690340065035