RADIOTHERAPY).
From the very earliest times sunlight has been considered an important aid in the pres ervation of health. The ancient Greeks and Romans exposed their naked bodies to the sun in the open air to recruit mental and physical energies, and built balconies or terraces (so lam) on the roofs or southern walls of their dwellings, so that the occupants could sun themselves. Exposure to the sun's rays was also adopted by the physicians of those times as a remedy for many affections, "especially dropsy, inflammation of the kidneys, and paral ysis." Celsus, the Latin writer, recommended for those with weak digestion a house "well lighted, having the winter sun"; but while he and Galen advocated sunlight as a remedial agent they pointed out the evils resulting from excessive insolation. Much has been written within the last century on the remedial value of sunlight. In 1815 Cauvin presented a thesis "on the benefits of insolation"; prior to 1820 Ebernier, Girard and others discussed the ef fects of sunlight on animal life; and in 1847 Richter, at Gottingen, wrote on "insolation, or the power of the sun on the human body." In 1848 Perreira spoke of solar light as a "vivify ing and vital stimulus," adding: "In maladies characterized by imperfect nutrition and san guinification, as scrofula, rickets and anaemia, and in weakly subjects with edematous limbs, free exposure to solar light is sometimes at tended with the happiest results." The importance of light for healthy growth and development has been recognized by san itarians for many years. Solaria or sun-rooms are a part of some modern hospitals. Houses and rooms receiving little or no sunlight are unhealthful. In a military barrack at Saint Petersburg the mortality was three times greater on the dark than on the light side of the building. Animals and plants living in the dark become bleached, as is celery. Clinical observations show that a want of sunlight pro duces depression of spirit, lack of energy, loss of appetite, disturbance of digestion, turbid urine and a kind of homesickness. The face becomes pale (etiolation), the blood is thin, the red corpuscles are diminished, pulse is frequent and weak, palpitations of the heart occur on the slightest exertion, there is muscular debility, little recuperative power, and an increased sus ceptibility to contagious diseases.
Interesting experiments and observations have been made as to light, by Becklard, Becquerel, Draper, Edwards, Gardner, Hunt, Landgrebe, Hammond and others; but, as one of the writers observes, "we do not know what is the exact effect produced by light. Does it," he inquires, "act directly, or is its only effect to modify the intensity of certain functions, such asthat as Later Edward Smith is a powerful stimulus to ((under the influence of day- light atmospheric air enters the lungs than under darkness or even under ex posure to artificial lignt.° Hence the vigor of
the "ruddy, healthy peasant who retires to rest with his cattle and is up with the lark° is be lieved to be mainly due to the thorough oxy genaion and subsequent reddening of the blood by much contact with oxygen in the light and air of the day. Where direct sunlight cannot be obtained in rooms, reflected sunlight by means of mirrors has been found serviceable, in the maintenance of health. A room with a southern exposure is desirable. Sternberg and others have shown that bright sunlight, inde pendently of the heat of the sun, is germicidal, destroying various pathogenic organisms, some times within a single hour. Sunlight is thus an important disinfectant. The sterilizing in fluence of light in the purification of water and sewage has been repeatedly proved (see STER nazAnoN). But the fact that the germicidal property of light chiefly depends on its blue and violet rays was proved by Finsen near the close of the 19th century. It has been recently stated that the strongest sunlight has too feeble bac tericidal properties for therapeutic purposes; for example, it does not kill bacterial skin-dis ease in the summer; but a concentrated focused light, transmitting as many blue, violet and ultra-violet rays as possible, such as the con centrated electric light of Finsen, is necessary. This light kills bacteria in a few seconds when spread on a thin film of agal. But Angell in 1878 had reported cases of acne speedily cured "by exposure to direct and entire sunlight.° Light has long been considered a complex agent. It has been known that the sunbeam is resolvable into rays of various colors (violet, indigo, blue, yellow, green, orange, red), which embody luminosity, heat and actinism, the chemical property of light. It was known that the red rays of the spectroscope were heat rays; that the rays toward the violet side were actinic or chemical; that luminosity was strong est in the orange and yellow rays. Later it was discovered that there are invisible heat rays beyond the red, and actinic rays beyond the violet, and these were called ultra-violet. About 1845 Gardner and R. Hunt experimented with the rays separated by a prism, and ascer tained some interesting facts as to the effects of blue, yellow and violet rays upon vegetation. Ponza, an Italian physician, found blue and vio let light to be soothing to the insane. Gen. Alfred Pleasanton, in his advocacy of blue light as an invigorator, claimed too much for it, and the "blue-grass° craze died out Most physicians believed that treatment by isolated rays of light did not possess "very essential therapeutic value.° A few clung to the idea that if the excess of heat and light could be eliminated the actinic rays might be of value.