Vol. Ⅰ The effect given to the blood picture and the function of the reticulo-endothelial system using reticulo-endothelial system blocked by the Indian ink method and also the tumor growth, survival rates and metastasis after transplanting Yoshida sarcoma cells intramusclarlly in the albino-rat thigh were examined. Experiment was done to find out the relations between the reticulo-endothelial system and the latter, which the results were as follows: 1) As formerly reported, the reticulo-endothelial system blocked by the Indian ink method showed anaemia by a certain quantity of ink but it passed by and restored gradually. It showed parallel relation with the function of the reticulo-endothelial system. 2) If the ink was small in quantity, it did not give much effects to tumor growth though the function of the reticulo-endothelial system was low. 3) The reticulo-endothelial system blocked by the Indian ink method had a connection with the growth of tumor to some extent and gave pictures which accelerated its growth. And stromal reaction near the tumor was weak. 4) Using the reticulo-endothelial system blocked by the Indian ink method, the appearance of the reticulo-endothelial cells in the tumor tissue was less compared with the control. Vol. Ⅱ Chapter 1 To prove the reaction on the X-rays of the reticulo-endothelial system and tumor growths, the author made an experiment based on the idea of tumor-host relationship. X-rays, 600r a day continuing 5 days totalling 3000r, were irradiated into the tumor bed, albino-rat thigh, and then Yoshida sarcoma cells were transplanted on the irradiated part. The influence against tumor growth, survival rates and metastasis were examined and the effects were found as follows: 1) Compared with the control, the tumor growths were restrained in the order of transplanted groups of the next day after irradiation, transplanted groups of 10 days after irradiation, and transplanted groups of 30 days after irradiation. With the survival rates, life extension could be recognized in the same order. 2) Stromal reaction could be strongly found in pre-irradiated groups, especially in these being transplanted the next day. Reticulo-endothelial cells could be found many compared with the control. Above all, it could be presumed that in case of preoperative irradiation, the part of reticulo-endothelial cells which has not been infiltrated by tumor cells shows protection system by stromal reaction. Chapter 2 When the tumor which was transplanted by Yoshida sarcoma cells became a regular induration; the size, the rise and fall, and the survival rates were examined by irradiating 300r a day for 10 days totalling 3000r. The effect showed that when the function of the reticulo-endothelial system which is one of the living body reaction was irradiated after it was restrained, the irradiation effect was less than the non-treated group. Consequently if the function of the reticulo-endothelial system would be irradiated after it was accelerated, it would obtain satisfactory result to medical treatments.