334 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1925 



the mercury vapor lamp. "Water, fat, starch, sugar, mineral oil, 

 glycerine, can not be so activated. Oils retain their acquired anti- 

 rachitic power for months. It has been claimed that " active " 

 food substance on oxidation gives off ultra-violet raj^s, but this is 

 not so. The error has arisen through the fluorescence of certain 

 quai-tz screens used in the photographic tests (A. AVebster). Drum- 

 mond has shown that radiated cholesterol makes an extremely active 

 radiated rats absorb this from the skin. The antirachitic vitamine 

 activated b}^ radiation this is the activated body. Probably too, 

 radiated rats absorb this from tlie skin. The antirachitic vitamine 

 or vitamine D is then sterol activated by radiation. 



We have no evidence so far that radiation can endow an inactive 

 food with the growth qualities pertaining to vitamin A. If thin 

 vrere possible, the margarine makers would have found a fresh source 

 of fortune in being able to claim that their product was made equal 

 to butter. Kickets can be prevented by making the diet more ade- 

 quate — e. g., by cod-liver oil — and also by teaching mothers the need 

 of exposing infants' and children-s bodies to the sunlight and by the 

 use of artificial sun baths at infant welfare centers. 



Prolonged exposure to intense ultra-violet rays either of the sun 

 or an arc light produces destruction and sloughing of the white skin. 

 While the visible rays, beside their heating effect, have no lethal 

 effect on the normal living animal cell, it is easy to produce a most 

 powerful effect from these rays by sensitization of the cells. Many 

 fluorescent dyes have this effect, eosin, erj^throsin, etc., forming a 

 compound with the bioplasm and so making the latter absorb and 

 be affected by rays longer than the ultra-violet. The action of visible 

 rays on sensitized cells depends on the presence of oxygen. 



The most interesting .sensitizer is htpmatoporphyrin, an iron-free 

 derivative from hemoglobin, closely allied to phyloporphyrin, a 

 derivative of chlorophyll. Traces of porphyrin (uro or stereo) are 

 present naturally in the body and may possibly give to the skin 

 some very slight natural sensitivity to visible rays. An excess of 

 porphyrin is present in some rare individuals endowing them with 

 an unfortunate sensitivity which causes skin eruptions and even 

 ulceration of extremities on exposure to bright light — a disease 

 called hydroa aestivalis, which has to be met by the greatest care 

 against their exposure to sunshine or bright daylight. 



When the mesentery is exposed in a cool glass irrigation chamber 

 to concentrated visible rays of an arc, no effect results, the ultra- 

 violet rays being filtered off by the glass. Add now a trace of 

 hffimatoporphyrin to the bath (1 in 10,000) and in a very few 

 minutes stasis occurs in the blood vessels. The lymphocytes gather 



