Of late years physicians and others, both here and in other countries, notably Denmark, Germany, and America, have accepted and striven to bring within the range of practical therapeutics the incalculably health-giving and remedial power of heat and light. This subject will be touched on in another chapter in connection with the exposure of the body to the air, while part of it is too special (as, for instance, the treatment of lupus with the violet rays of the spectrum) to be more than alluded to. The principle of it all is that light is as tonic to the body of a man as it is to a plant, and that just as a plant is sickly and pale if given insufficient light, so the body if stinted in this becomes weakly and inefficient, a cellar-grown plant. Following this clue, experiment has established beyond doubt that for anæmia of certain kinds the best possible remedy is exposure to heat and light, and in Germany there is more than one sun-cure for this, the course of treatment being that patients pass hours in the sun every day with practically no clothes on. Here in England, and especially in London, such treatment is seldom possible, the two great drawbacks being lack of sun and lack of privacy[11], and in consequence artificial light has been resorted to, not as being better than sunlight, but as the best substitute for it. Here the body is exposed to a violent illumination of electric light (the eyes and head being protected), and is given a light-bath in the same way as a Turkish bath gives a purely heat bath. Incidentally, it is true, the bath of electric light is extremely hot (a temperature far above that of the ordinary Turkish bath being reached without inconvenience or danger), but the main object is to administer the tonic of light, and of that which light becomes when it has passed through the surface-skin. Of its extraordinary effects in cases of anæmia, for instance, it is outside our province to speak, but in a modified form, _i.e._, by exposure when possible of the body to sunlight, and the constant and unvarying desirability of living in light rooms, much of its beneficial effects can be enjoyed, and should be, by everyone. Indeed, to take the long continued effect of light, not on an individual but on a race, how much of the gaiety of the southern nations may perhaps be directly due to sunshine? Certainly “a gloomy house,” or “a gloomy room,” is gloomy in more senses than one, for instinctively light affects the spirits; it is tonic and invigorating to body and mind alike, and ten minutes of exposure of the whole body to the sun, fantastic as it may sound, is as great a dispeller of shadows as is the sun itself.