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Principle of the Knott Hemo-Irradiator is simple. A small amount of blood (two cubic centimetres per pound of body weight) is withdrawn from a vein in the arm, mixed with citrate to prevent clotting. The citrated blood is passed through a rubber tube into a small, round quartz and steel irradiation chamber. Against the quartz window the doctor fits a lamp, like a flashlight, which emanates ultraviolet rays. An automatic shutter turns the lamp off every few seconds to prevent over-irradiation. Length of irradiation varies from nine to 14 seconds, depending upon the severity of the infection. Once the blood is delicately irradiated, it is returned immediately to the same vein.
Often several exposures are necessary during the course of an illness. An irradiation takes less than 20 minutes, and patients who are able to walk can go about their business after resting half an hour.
Although irradiation combats a great many of the same infections as chemotherapy, it has none of the harmful aftereffects of sulfanilamide and sulfapyridine. "Irradiation," said Dr. Miley last week, "has never hurt a patient yet."