Numerous investigations have shown that light exerts an influence upon the endocrine functions, especially upon the sexual cycle. It is likely that light may stimulate the hypophysis to an increased gonadotrophic activity, and that this effect is mediated through the eyes. Beside this «physeal reaction», light might produce some endocrine effects as a result of irradiation of the skin. Thus Myerson & Neustadt (1939) found that ultraviolet irradiation of the skin increased the 17-ketosteroid excretion in man.
This observation was especially interesting, as it might be a clue to the problem of the manner in which ultraviolet irradiation exerts its beneficial effect upon certain skin diseases. A photo-chemical steroid formation could be an important factor.
Myerson & Neustadt used a small quartz, mercury lamp, the spectrum of which consisted of 52 per cent infrared, 20 per cent luminous and 28 per cent ultraviolet rays. (No further information on the