EFFECTS OF X-RAYS PRODUCED AT 50 KILOVOLTS ON DIFFERENT SPECIES OF BACTERIA1

The present article concerns an investigation of the effects on different species of bacteria of X-rays produced at 50 kv. The object of the investigation was threefold: (1) to determine the rate of destruction of the bacteria by the X-rays, (2) to determine the effect of different initial concentrations of bacteria on the rate of destruction, and (3) to determine the dosage of X-rays necessary to destroy 63 per cent of the bacteria (or, conversely, the dosage permitting 37 per cent sur-vival). This dosage is known as the "37 per cent dose " or the "mean lethal dose." MATERIALS AND METHODS Equipment. A Wappler Roentgen apparatus, Bellevue model, utilizing a Machlett3 berillium window X-ray tube and operating at a peak voltage of 50 kv, was used in this study. To cut off the longer wave-length portions of the spectrum, filtration with four sheets of aluminum foil (each 0.00065 of an inch thick, i.e., 0.0026 of an inch in total thickness) was used. Measurements of dosage were made according to the procedure described by Proctor and Goldblith (1949). Organisms. The following organisms were exposed to X-ray irradiation: (a