62 EFFECTS OF IONIZING RADIATION is due to a neutrophilic leukocytosis. c) The drop in lymphocytes is early and profound. Jiittle or no evidence of recovery may be apparent several months after exposure, and return to normal levels may not occur for months or years. d) The platelet count, unlike the fluctuating total leukocyte count, falls ina regular fashion and reaches a low on the 30th day. Some recovery is evident early; however, as with the other elements, recovery may not be complete several months after exposure. 4. As an index of severity of exposure, particularly in the sublethal range, the total white or neutrophile counts are of limited usefulness because of wide fluctuations and because several weeks may be required for maximum depression to become evident. The lymphocyte count is of more value in this regard, particularly in the Jow dose range, since depression occurs within hours of exposure. However, since a marked depression of lymphocyte counts occurs with low doses and, since further in- crease in dose produces little more depression, this index is of little value at the higher doses. 5. Platelet counts showed a regular pattern of change in the present studies, with the same time of maximum depression in all exposure groups and with the degree of depression roughly proportional to the calculated doses. It appears, therefore, that the platelet count has considerable promise in the sublethal range as a convenient and relatively easy direct method of determining the degree of exposure. References 1. Brecher, G., and Cronkite, E. P.: Morphology and Enumeration of Human Platelets, J. of Applied Physiology, 3: 365, 1950. w 2. Walsh, J. E.: Applications of Some Significance Tests for the Median Which Are Valid Under Very Jeneral Conditions, J. Amer. Stat. Assoc,, 44: 342- Co cof CFA 350, 1949. 3. Rosenbaum, 8.: Table for a Nonparametric Test of Location, Annals of Math. Stat., 25; 146-150, 1954. . Rosenbaum, S.: Tables for a Nonparametric Test of Dispersion, Annals of Math. Stat., 24: 663-069, 1953. . Dixon, W. J.: The Statistical Sign Test, J. Amer. ot The initial rise in total white count Stat. Assoc., 41: 557-566, 1946. . Quenonille, M. H.: Associated Measurement, Chapter 3, Ordering Test, Academic Press Inc.. Publishers, New York, 1952, . White, C.: The use of ranks in a test of significance for comparing two treatments, Biometrics st or more. 8:33, 1952. . Moses, Il. E.: Nonparametric statistics for psychological research, Psych. Bull. 49:122, 1952. . Wintrobe, M. M.: Clinical Hematology, Lea and Febiger, Phil., 1951. 10. Standard values in blood, Air Force Technical Report No. 6039, 1951. Published by National Academy of Science. 11. Minot, G. R., and Spurling, R. G.: The effect on the blood of irradiation, especially short-wave length Roentgen raytherapy, -im. J. Med. Sci. 168: 215, 1924. 12. Oughterson, A. W., and Warren, S8.: Medical effects of the atomic bomb in Japan. McGraw-Hill Book, Inc., New York, 1956. . LeRoy, G. V.: Hematology of atomic bomb casualties, Arch. Int. Med. 86: 691, 1950. 14, Jacobson, L. O., Marks, E. R., and Lorenz, N.: Hematological Effects of ionizing radiations. Radiology 52: 371, 1949. 15. Cronkite, E. P., and Brecher, A.: The protective effect of granulocytes in radiation injury, Ann. N.Y. cad. Sci, 59: 815-833, 1955. 16. Snell, F. M., and Neel, J. V.: Hematologic studies in Hiroshima and a control city two years after the atomic bombing, Arch. Int, Med. 84: 569, 1949. 17. Yamasoiva, Y.: Hematologic studies of irradiated survivors in Hiroshima, Japan, Arch. Int. Med. 91: 310, 1953. 18. Hempelmann, IL. H., Liseo, H., and Hoffman, J. G.: The acute radiation syndrome: A study of nine cases and a reviewof the problem, Ann. Int. Med. 36: 279, 1952. . Hasterlik, R. L: Clinical report of four individuals accidentally exposed to gamma radiation and neutrons, Argonne National Laboratory, Jan. 1953. . Cronkite, E. P., and Brecher, G.: Defects in hemostasis produced by wholebodyirradiation, Josiah Macy, Jr. Foundation, Transactions of the fifth eonference on blood coagulation, New York, 1952.