As was reported in the Okayama Igakkai-Zasshi last year, an inquiry of mine into the influence of the spleen and the thyroid gland upon the blood-picture has proved the fact that it is the blood-platelet, which undergoes the most remarkable changes, in other words, that there exist, even through the blood-platelet a certain antagonistic function between these two organs. Then, having examined by various procedures the numerical and morphological changes of the blood-platelets in arteries and veins of the spleen, such results as following were attaind. 1) In the case of normal rabbit, the number of blood-platelets in splenic veins is far less than those in splenic arteries, and the blood-platelets which decrease in number are, for the most part, those of smaller types. This numerical difference becomes indistinct when thyreoidin is given or silver-elecroid injected continually, while morphologically no remarkable changes occur. On the other hand, when adrenalin is injected, the difference between the number of the blood-platelets in veins and those in arteries of the spleen diminishes slightly, while the number of the smaller blood-platelets in veinous blood increases. 2) After the thyroidectomy and the injection of phenylhydrazin, the number of the blood-platelets in splenic veins obviously exceeds that in splenic arteries, and morphologically that of the larger ones increases.