Radiation Sickness in the Monkey

Abstract

Much of the animal experimentation in the field of ionizing radiation has been directed toward the solution of practical problems relating to man, either in therapy or nowadays in industry and possibly warfare. In view of this interest, it is surprising that subhuman primates have been used so little as subject animals. A few investigators have worked on portions of the monkey's body (1, 2, 3), but the effects of total-body irradiation seem to have been described only by Dowdy (4). The following observations on clinical and pathological findings in the macaque subjected to total-body x-irradiation are given to help fill this gap between the knowledge on lower animals and man. Hematologic and electroencephalographic findings in these same animals have been presented in detail elsewhere (5, 6). Method Thirty-seven monkeys (Macaca mulatta) of both sexes and weighing from 5 to 7 pounds were irradiated. Non-irradiated animals were used for comparison in interpreting autopsy findings and as controls for the detection of epidemics within the colony. Only healthy animals were used and all but 10 had been tuberculin-tested. They were caged separately and fed on a balanced mash diet supplemented with ascorbic acid. They received no antibiotics or parenteral fluids. For two to eight weeks prior to irradiation and during the survival period after irradiation, daily notes were taken of behavior, appetite, and character of stools. Physical examinations were made before irradiation, two to three times per week during the immediate post-irradiation period, and less frequently thereafter. These included observations on general nutrition and activity, on skin, hair, conjunctivae, oral and anal orifices, regional lymph nodes, and on liver size. Necropsy examinations were performed, of which only the gross results are presented here. Non-metallic restraints were used during irradiation to hold the unanesthetized animal in a wooden seat, which was enclosed by a 1 × 1 × 3-foot box of 1/8-inch plastic, liberally supplied with holes for ventilation (Fig. 1). To insure even exposure, the box was turned by a motor at a rate of 1 r.p.m. Control animals confined in this manner and revolved for two hours showed no ill effects. The axis of rotation of the animal was 100 cm. from the horizontally directed outlet of a 250-kv. G.E. Maximar x-ray unit. Employing 15 ma. with 0.5 mm. Cu and 1.0 mm. Al filters, the half-value layer was determined to be 1.7 mm. Cu. Variation in intensity in different parts of the field as measured by five calibrated thimble chambers (100 r) was less than 4 per cent of the mean value. Runs made with a calibrated thimble chamber inserted in an axial hole in a masonite cylinder 8 cm. in diameter and 15 cm. long, and rotated in the plastic box, indicated a dosage rate of 13.7 r/min. Monkeys received single doses of 400 r (8 animals), 550 r (1 animal), 600 r (10 animals), 700 r (12 animals), or 800 r (6 animals).3