first place, at all events, is destructive and harmful in a high degree, is now clearly established by the observations and experiments of Charcot, Unna, Hammer, Bowles and others, while Finsen has made an important advance in the treatment of disease based on this fact. The conditions called 'sun-burn,' 'snow-burn' 'snow-blindness' for instance, which may affect even travelers on snow-fields and Arctic explorers, are now known to be wholly due to the violet and not to the red rays. Unna's device of wearing a yellow veil, and Bowles's plan of painting the skin brown, thus shutting off the violet rays, suffice to prevent sunburn. The same effect is also obtained by nature, which under the stress of sunlight, and largely through the irritation of the violet rays themselves, weaves a pigmentary veil of yellow and brown on the skin, which thus protects from the further injurious influence of the violet rays and renders the sunlight a source of less alloyed joy and health.
That the presence of the red rays, or at all events the exclusion of the violet, is of great benefit in many skin diseases seems to be now beyond doubt. This has been shown by Finsen in his treatment of smallpox in red rooms; it appears that it was also known in the Middle Ages as well as in Japan, Tonquin and Roumania, red bed-covers, curtains or carpets being used to obtain the effect. Under the treatment by red light not only is the skin enabled to heal healthfully without scarring, but the whole course of the disease is beneficially affected and abbreviated, the fever is diminished and also the risk of complications. Another physician has discovered that a similar beneficial effect is produced by red light in measles. A child with a severe attack of measles was put into a room with red blinds and a photographic lamp. The rash speedily disappeared and the fever subsided, the child complaining only of the absence of light; the blinds were consequently removed, and the fever, rash and prostration returned, to disappear again when the blinds were resumed.
Whether red light, or the exclusion of violet, exerts a beneficial influence on the hæmoglobin of the blood and on metabolism generally has not been distinctly proved, but it seems to me to be indicated by such experiments as those of Marti published a few years ago in the Atti del Lincei. This investigator found that while feeble irritation of the skin promotes the formation of blood corpuscles, strong irritation diminishes the blood corpuscles and also the hæmoglobin; at the same time he found that darkness also diminishes the number of red corpuscles, while continued exposure to intense light (even at night the electric light, which, however, is rich in violet rays) favors increased formation of red corpuscles, and in some degree of haemoglobin. Finsen has shown that inflammation of the skin caused by chemical or violet light leads to contraction of the red corpuscles.
This brings us to the consideration of the influence of the red rays