Effect of X-Irradiation on Reticulo-Endothelial System **

The role of the reticulo-endothelial system (RES) in recovery following whole body X-irradiation has aroused considerable recent interest."5'17 However, ready explanation of this role is complicated by the fact that pertinent data concerning the effect of ionizing radiation upon the RES seem somewhat contradictory. 8 1, U U2"-8 Generally, the RES is regarded as a non-radiosensitive tissue.8'25 m Taplin, et al.,' reported very little effect of 300 r whole body X-irradiation on the RES of rabbits, basing their conclusions on the blood clearance of the colloidal dye, prodigiosin. Barrow and co-workers' were unable to demonstrate any change in the disappearance rate of intravenously injected colloidal gold into rabbits following 800 r whole body X-irradiation. On the other hand, Kogae' noted an alteration in uptake of carmine by the RES of rabbits after only 42 r whole body X-irradiation, and, after 25 to 50 r, Pape and Jellinek'2 reported degenerative cell injury in the spleen of rats. A technique has been developed by one of us9"-" for study of RES activity in laboratory animals by means of intravenous injection of radioactive colloidal chromium phosphate (CrP3204). The technique may be used in at least three ways: (i) Disappearance rate of radioactivity from the blood may be determined. Thus, one can obtain an over-all outlook of the activity of the whole RES. (ii) Distribution of radioactivity to different organs may be measured. Thus, the relative RES activity of various organs can be observed because, in normal animals, the distribution patterns of a CrP3204 suspension seems very constant.10 The liver, spleen, and many other organs remove a definite