In a recent communication we1 reported the results of a study of a group of infants irradiated during the winter months by means of the mercury vapor lamp. The object of the investigation was to determine primarily whether ultraviolet radiations diminished the occurrence of respiratory infection. It was shown that in spite of systematic exposures to these rays the incidence of these diseases was not altered.
It is thought that the frequency of respiratory infections during the winter is due in part to a deficiency of sunlight. The mercury vapor lamp emits an exceptionally large intensity of invisible or ultraviolet rays as compared to the sun, which produces only 1 per cent of these radiations. It is evident, therefore, that the rays of the mercury vapor lamp are by no means the counterpart of those of the sun. It is quite possible, as Hess2 has suggested, that there