The Penetrative Power of the Bactericidal Rays in the Ultraviolet Part of the Spectrum, as Emitted by Carbon C

More important than the inherent resistance of organisms, as an obstacle to the practical application of ultraviolet radiation therapeutically, are the low penetrative power of the bactericidal range and the avidity with which the rays are absorbed by organic matter. The penetrability of various glasses by the germicidal rays emitted by Carbon C was therefore investigated. The same materials and the same technique were employed as in previous experiments.' The petri dishes however, after being prepared, were covered with various glasses, and then exposed to the light emitted by Carbon C. The results in Table 1 demonstrated the usefulness of fused quartz, as it is very readily penetrated by the short rays. Results of ultraviolet transmission tests at the Bureau of Standards (1), upon a number of special glasses and common window-glass areas, follow (Table 2). Although, according to the figures compiled at the Bureau of Standards (1) and listed above, Corex apparently allows the penetration of 89 percent of long wave-lengths, the results of our experiments