Enhancement of the antirachitic and calcifying properties of milk by exposure to ultraviolet rays has raised the question as to whether or not there was a destruction of vitamin A. Data from various laboratories have been contradictory, but a review of such data shows that a wide difference in the technic of irradiation, particularly in reference to the period of exposure, was in all probability the cause of the conflicting evidence. For illustration, Titus and Hughes1 reported the apparent destruction of vitamin A in milk after an irradiation period of several minutes, whereas Supplee and Dow2 reported that there was no measurable destruction of vitamin A after an exposure period of only sixteen seconds, during which substantial antirachitic properties were imparted to the milk.
Further work on the irradiation of milk at this laboratory,3 wherein the physical characteristics of the radiant energy have been correlated with the