EFFECT of exposure of tuberculin to light.

This paper reports two studies dealing with the effect of light on the potency of tuberculin. In each study light-exposed and unexposed (control) samples from the same tuberculin dilution were compared by duplicate intradermal Mantoux testing in groups of BCG-vaccinated schoolchildren. The difference in mean size between the children's reactions to the two samples was used as a measure of the light-effect.In the first study, carried out in Egypt, a 5 TU dilution was exposed in ordinary, clear, glass bottles to subtropical sunlight for a total of 12 hours. Duplicate testing in 154 children showed that the exposed dilution had lost all but a fraction of its original potency.To obtain information on the relative effect of different parts of the solar spectrum 10 TU dilutions were irradiated with artificial light of different wave-lengths in a second study comprising 727 children. Ultra-violet radiation was found to have a strong effect on the potency of tuberculin whereas medium- and long-wave radiation of the same intensity had little or no effect. It is of practical importance that ultra-violet rays of the wave-lengths used in this study are transmitted by ordinary clear glass.From the reported studies it seems that prolonged exposure of tuberculin to strong sunlight and daylight should be avoided.