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A suitable substitute has been found for the ordinary glass Wood filter. The latter is advantageous in the diagnosis of fungous infections, especially those of the scalp. The substitute is a 250 watt light bulb with nickel and cobalt incorporated in the glass wall of the tube, which thus supplies radiation near the longer wavelength ultraviolet bands. It is made by the General Electric Company. This bulb was designed for the testing of minerals, paints and certain inks that have fluorescing properties. It is known as number 250 A-21-60 natural red purple, Purple X bulb. It sells for $1.25, and, although the filaments are fragile and may be broken easily in shipment, each intact bulb will last for at least fifty hours of intermittent use. It also has the advantage of fitting any medium light socket designed for 115 volts and operates on either alternating or direct current. However, since
DENNIE CC, MORGAN DB. USE OF THE PURPLE X BULB IN DIAGNOSIS OF FUNGOUS DISEASES OF THE SCALP. Arch Derm Syphilol. 1947;55(3):396–397. doi:10.1001/archderm.1947.01520030089014