Light therapeutics, both natural and artificial, is gradually assuming a more important place in the treatment of disease. Heliotherapy is now considered a curative agent par excellence for certain maladies. Michelet's old adage, "Of all the flowers, that which most needs the sun is the human flower," has been proved scientifically. Light as a curative agent has acquired its reputation largely within the last twenty years. But only within the last eighteen months has it been demonstrated how light might act on the animal organism. It appears that physiologically active substances which perfect the desired cure are produced by irradiation from inactive precursors in the foods or tissues of the animal. Drummond (1925) states that the evidence in support of this theory has gradually been forthcoming, and its unfolding constitutes one of the most remarkable series of events in modern biochemistry.
The use of light for the treatment of