SummaryNow, to summarize the above statements, in case of mental work such as mental arithmetics the α‐wave of ‐the brain tends to diminish its amplitude in one: hand arid to increase it:; frequency in the other hand. The mode and grade of reaction do not differ thereby from those of sensory stimulation. I However, there is a slight difference in the blockin:; time and the suppression course in both, which indicates a n aspect o f the mode of the human rnental work. Also it has been proved that the: change in the α‐wave at mental arithmetics is not altogether based on the accompanying optical factor. No particular variation of the α‐wave suppression was percc3ived at mental work in the different portion of tic. skull. By analysing the amplitude distribution curve a simple increase in excitability in the brain cortex was perceived during mental activity. As is stated in the introduction and as the. experment ofLontlmr*d, EidtoiAandLenizoxtells, the increase in the cerebral blood flow is perceived during mental work. Accordingly, the phenomenon of diminution of the amplitude and increase of the frequency in the brain wave tied up with increase of the brain blood flow may be looked upon as indicating one aspect of the brain activity during mental work. In this case whether the increase of tile brain blood flow causes the change in the α‐wave or, in reverse, the changed tone of the nerve cell effecting changes in the α‐wave. causes secondarily the acceleration of the brain blood flow remains still undecided. However, the fact that even though the brain blood flow is passively increased by aderenalin injection no remarkable change was perceived in the lT‐wave, offers basis to the supposition that the change of the α‐wave is primary. Only, existence of the distinct α‐wave difference between sensory activity and purely mental activity is not yet ascertained. Concerning the brain blood flow there isGerards30report where a simple optic stimulus is sufficient to cause a n increase in the blood flow in a part of the opticalarea, which speaks for the. supposition that increase of the blood flow can occur accompanying both sensory as well as mental activities. Also in case of the α‐wave the diminution of amplitude and the increase of frequency occur both at sensory and mental activities, whereby there is noticable among them certain difference in the time course and a few other moments. Lastly the thesis that the diminution of the α‐wave amplitude is primarily caused through excitement of nerve cell may appear to be less founded or rather contradicting, t d clarify which pointJasper's30)energy theory may serve helpin