PHOTOTHERAPY (from ( cluis,phos, light Oepavela, th era pcia, cure, from deparetietv, thera peach', to cure, from Oepcin-wv, Meru attendant). Treatment of disease by means of light. The method of applying light for thera peutic purposes, devised by Dr. Niels B. Finsen, of Copenhagen, about ISM, is founded on the fol lowing data : (1) The bauterioidal property of the chemical rays of light; (2) the power of the chemical rays of light to produce an inflamma tion of the skin (sunburn, erythema solare); (3) the power of the chemical rays of light to pene trate the skin. The violet and ultra-violet rays of light obtained from the sun or from an electric are-lamp will, in a few hours, kill phite cultures of Bacillus prodigiosus at a great distance. The so-called sunburn is not a burn. If sunlight or electric light. be passed through a layer of dis tilled water so arranged as to cut out the ultra red rays (the dark rays of heat). the resulting skin-inflammation is as great as if the light were uncontrolled. If sunlight be thrown upon the skin through a glass screen which cuts out the violet and ultra-violet rays, there is no resulting inflammation. Again, if small sealed bottles con taining muriate of silver be placed under the skin of some animals kept in the dark, and of some animals exposed to the sun, if the tubes be re moved .an hour later, it will be found that the muriate of silver is blackened in the cases of the animals which were exposed to the sunlight. hut not in the cases of those kept in the dark. It is shown by experiment that the chemical rays of light penetrate more easily in bloodless tissues than in those filled with blood. In a piece of sensitized paper put against the back of a man's ear upon the front of which the blue and violet rays are allowed to fall for 5 !ninnies, no reaction takes place. If the paper be replaced and the ear be compressed tightly bettveen two glass plates and exposed again to the same light. the paper will be blackened after 20 second, exposure. In the treatment of patients, sunlight is used in the summer, when the sky is bright, hut otherwise the light of electric are-lamps of 50 to Su amperes is employed. Concentration of the light is neces sary to render it powerful as a bactericide. To avoid burning the skin, the light must be colored. To make the sunlight strong and cool Finsen de vised a special apparatus, consisting of a lens about 20 to 40 centimeters in diameter. The lens, composed of a plain glass and a curved One, is framed in a brass ring, with a bright blue. weak ammoniacal solution of sulphate of copper between them. The water absorbs the ultra.-red rays and, being blue, it excludes much of the red and yellow rays. The excluded heat rays have little bactericidal power; whereas the blue, yhdi t. and ultra-violct rays are but slightly impaired in chemical or bactericidal power. The lens is so that it can be raised and lowered as well as turned on a vertical and horizontal axis, by which means it can be placed perpendicularly to the sun's rays. and at such a distance as to make
the light strike the diseased area. For concen trating the electric arc-light Finsen devised an apparatus consisting of lerscs of quartz framed in 11\ 0 the one within the other. Quartz allows the ultra violet rays (even those of very short wave-length) to pass through it much more easily than through glass, and these rays from the eleetrie light are of less length than those from sunlight. Faring the lamp are placed two lenses having together a focal distance of 12 centimeters. At this dis tance front the lamp. those lenses will concen trate and render parallel the divergent rays from the lamp, and direct them through the brass tithes, at whose distal end they strike two quartz lenses. These lenses concentrate the parallel rays eonverge them till they are united about 10 centimeters beyond the outer lens. The space between these latter lenses is filled with distilled water which absorbs the ultra-red rays, lint does not impair the blue, violet, and ultra-violet rays. Surrounding this end of the apparatus is a man tle. through which cold water flows to prevent boiling of the distilled water between the lenses. In spite of all this precaution, the light is still too warm, and the skin must he cooled to avoid burning. This is effected by an apparatus con sistiim of a plate of quartz and a plain con vex lens of quartz. both fitted into a conical brass ring, which carries two small tubes and four arms. To •-ash arm is fastened an elastic band by means of which the apparatus is pressed against the skin, Cold water is run into one tube and nut of the other, and thus the skin is cooled so that it can tolerate the strongest light. The pressure of the planwconvex lens on the skin renders it anaemic. thus fitting it for the easy penetration of the cheinival rays. A small area of the skin is treated for an hour each day. The skin swells and becomes red, and a India may appear; but sloughing has not resulted. During the application the nurses are obliged to weal to protect their eyes from the bril liant light. Dilatation of cutaneous vessels by the violet rays may continue for six months.
di-oases of ,Oppo:oi /Met Prial origin have been treated by this method. but cures have re sulted only in of lupus rulgaris, lupus cry aintosits, ohnarirt «reatn, crud careinoma. The greatest sneers.- has been rcaehed in eases where there was an absence of searrimz, of pigmentathin, of great vaseularity, of great depth below the surface, of involvement of eyelid or mucous mem branes, or of great extent of lesion.
The number of patients at Einsen's Institute has Mere:I-ell from seven in 1897 to an unnum bered elientfle. with over a hundred on a waiting, list. A Brooklyn. N. Y., physician tins opened an institute for Einsen's treatment. The Roent gen or N•rays (q.v.) penetrate to deep layers not reached by sunlight or electric light. Consult Morris & INwe. "Einsen's Eight Treatment of Lupus and Rodent Ileer," in British Medical Jour-nut. February 9. Mi.