398 ANNUAL. REPORT SMITHSONIAN INSTITUTION, 19 3 2 



posture to red rays caused a loss of antirachitic property. Likewise, 

 old, ineffective ergot preparations could be reactivated on exposure 

 to ultra-violet, but subsequent irradiation with red rays again de- 

 stroyed the efficacy. On the other hand, the estrus hormone could be 

 destroyed by ultra-violet but reactivated by red rays. 



In short, a summation of the mode of action of light in the present 

 state of our knowledge is difficult. The isolated experiments carried 

 out on single cells, on bacteria, on the components of cellular struc- 

 ture, and so on, are difficult to carry over and apply to the effects on 

 the human body. Certain rays do penetrate directly to the capil- 

 laries, but their effects can only be assumed through such action. 

 Vitamin D-like substances are definitely formed, but their effects on 

 the body, except in disturbances of calcium metabolism, are unde- 

 fined. Increased cell permeability as a result of light exposure can 

 be demonstrated, which may imply improved cellular nutrition. 

 Exact effects on the other components of the skin and on the various 

 skin functions, or directly on the blood circulation and so on the body 

 functions, must still remain for future investigation to define 

 accurately. 



LIGHT AND MOVING AIR FROM OUTDOORS 



The application of light necessarily requires consideration of ac- 

 companying moving and open air. With lamps, moving air from 

 outdoors should be employed if possible. Air movement produces 

 increased heat radiation and conduction with better respiration and 

 excretory function of the skin. Cool moving air acts directly on the 

 vasomotor system, stimulating the superficial capillaries, producing 

 a hyperemia and, in turn, a depletion of the cutaneous circulation. 

 This, acting as a massage, may be responsible for the development of 

 muscle, otherwise immobilized in treatment. With sunlight therapy 

 the effect of moving open air is greater, but air exposures may well be 

 utilized with artificial light therapy through satisfactory ventilation 

 of the treatment room. Carbon arc lamps may be effectively used 

 outdoors in cloudy, warm weather. However, chilling should always 

 be avoided, even at the expense of losing the air movement when one 

 is employing artificial sources of light. 



SUNLIGHT VERSUS CARBON ARC AND QUARTZ MERCURY VAPOR ARC LAMP 



In mid latitude, sea-level stations, during midsummer, clear mid- 

 day sunlight contains intense ultra-violet rays down to 297 milli- 

 microns. Those around 290 millimicrons, its lowest limit, are in 

 intensity about one-millionth of those around 310 millimicrons. Its 

 emission of visible and infra-red energy is very high. 



Proponents of solar therapy have insisted on the use of radiation 

 having a spectrum with components relatively like those of sun- 



