For the purpose to study changes in the metabolism of RES in vivo under anesthesia over a long period a series of experimental observations were conducted with dogs by means of Glycyrrhizin (59)Fe-colloid method and the following results were obtained. 1. It was found that to the dog under anesthesia the phagocytosis of the RES is clearly inhibited, and with the use of Isozole it is slightly inhibited, while deep anesthesia such as combination anesthesia and low body temperature anesthesia distinctly affects the phagocytic function of the RES. 2. On the other hand, in the study of the hemoglobin synthesis which reflects the metabolic function of the RES, by means of fractionation of hermin iron and non-hemin iron in erythrocytes it was demonstrated that the hemoglobin synthesis is clearly inhibited by anesthesia and deep anesthesia inhibits the synthesis to a greater extent. 3. Simultaneous observations of the total organic iron, hemosiderin, ferritin fractions revealed that under anesthesia the retension of hemosiderin is increased, ferritin is decreased, and the ratio of hemosiderin to ferritin is lessened, suggesting that there develops a retension phenomenon in the RES. 4. The metabolic function of the RES is markedly inhibited by the low body temperature anesthesia at 27℃ to 28℃ but along with the lapse of time there develops an adaptation-recovery
phenomenon and the metabolic function is inhibited more markedly rather than phagocytosis but it does not reach the stage of arresting the reaction. These findings clearly demonstrate that the Glycyrrhizin (59)Fe colloid method is a superior one for examining the functions of the RES to the classical method available. Further, in the investigation of the RES by this method it has been suggested that the function of RES is less inhibited by shallow anesthesia while by the deep anesthesia its inhibition is greater, and that under the low body temperature anesthesia more of the primeval function of the RES is maintained, thus rendering many useful criteria of clinical importancs.