The author made an experiment in order to determine whether the spleen has any connection with the formation of socalled Traube-Hering's blood pressure curve. Since Roy observed the rhythmical contraction of the spleen, many experiments have been made with the purpose of solving the above problem, but they were all made after opening the peritoneal cavity, so that the blood vessels of the abdomen were exposed to the air, therefore the results may have been greatly influenced by the abnormal conditions of this exposure. A dog and a rabbit, from which the spleen had been previously cut out, were anaesthetized with morphine and urethan respectively, and the canula was placed in the carotid artery, and then connected with a mercury manometer. Artificial respiration maintained pulmonary ventiation after an intra-venous injection of curare. The interruption of artificial respiration caused a gradual rise of blood pressure and a typical Traube-Hering's wave in the blood pressure curve. These results confirm the theory that the spleen has nothing to do with Traube-Hering's wave.