204 ANNUAXi REPORT SMITHSONIAN INSTITUTION, 19 30 



SUNLIGHT CAN NOT BE STANDARDIZED 



As the ultra-violet rays in sunlight vary, not only according to the 

 season and the time of day, but also according to atmospheric condi- 

 tions it is utterly impossible to determine with any degree of accuracy 

 the dosage of sunlight needed in specific cases. Hence the helio- 

 therapist has learned to proceed cautiously and experimentally. A 

 sun bath of an hour may be safe enough on a certain day, but may, 

 at the same hour, and in the same length of time, on the day follow- 

 ing, cause a severe sunburn. One can not standardize sunlight with 

 precision. In this respect, certainly, the ultra-violet lamp offers 

 an advantage. For with the same apparatus, and with the distance 

 from the lamp also the same, the time of irradiation practically 

 determines the dosage. This dosage is now being worked out, al- 

 though, of course, we must remember that some persons are much 

 more susceptible than others to the radiation, just as individuals 

 differ in their tolerance of our common drugs. 



IRRADIATED FOODS 



The substance in the skin which responds to the ultra-violet is asso- 

 ciated with cholesterol, and a similar substance is found in certain 

 plants associated with phytosterol, which suggested that probably 

 the vitamin could be produced in certain foods by irradiation, thus 

 making unnecessary the ingestion of the unpalatable cod-liver oil. 

 Irradiated grain foods, irradiated milk and similar products have 

 given promise of usefulness. Such irradiated foods are now on the 

 market, as are also concentrated products obtained by treating an 

 impure ergosterol with ultra-violet rays. The dose of the latter 

 product is extremely small, and an overdose is harmful. It is said 

 to represent 100,000 times its weight of cod-liver oil as far as the 

 antirachitic effect is concerned. Strange to say, however, when ergo- 

 sterol, or a food containing it, is irradiated too long, the vitamin 

 becomes inactive. Indeed, the whole study of irradiated foods, and 

 of cod-liver oil substitutes generally, is still in its infancy, and much 

 remains to be learned, if not in regard to the technique of their prepa- 

 ration, then certainly as regards proper dosage. A preparation of 

 irradiated ergosterol has been approved by the council of pharmacy 

 and chemistry of the American Medical Association, and may be ac- 

 cepted as quite reliable. But such products should be considered as 

 medicine, to be taken under medical supervision. 



USE OF LAMPS 



The same cautious course should be followed also in the employ- 

 ment of ultra-violet radiation when this is produced artificially. We 

 know that sunlight does not ordinarily harm us if we avoid sunburn. 

 But the radiation from arc lights or mercury vapor lamps embodies 

 the wave lentrths shorted than those found in sunlight which comes 



