hand not employed were clinched, and all the expressions indicated great tension. The second set of tracings, gained from a girl, E. H., twelve years of age, shows evidences of marked fatigue after a few hours' work; but the effect upon the bodily activities is quite in contrast with that of the case just mentioned. Here there was relaxation of the muscles, a general letting go of the whole body, revealed in the tracings taking an abrupt downward direction. The third group of tracings was gained from W. R., whose characteristics have already been adverted to, and who indicated here, as in the other tests, that his morning's duties had had no serious effect upon his nervous energies. [Illustration: M. L. R.] [Illustration: E. H.] [Illustration: W. R.] It should be said in passing that the principle of healthful mental growth and activity seems to require that in education of any sort cerebral cells should be freely exercised up to the point of fatigue, but never beyond; for after this there is not only no progress, but what has been gained by previous training may even be lost. And, what is more serious, the undue depletion of the nerve cell renders its recovery extremely slow, and investigation has shown that school children when overtaxed return to their studies day after day in a fatigued condition, their energies not being fully restored until the long vacation brings the needed rest.[33] Those who train athletes realize that the fatigue limit must not be passed if possible, and this law is recognized as well in the training of racing horses,[34] One who has observed his experience in learning to ride the bicycle must have discovered that practice pursued when in a condition of exhaustion operates rather to retard than to promote facility. So in matters of the mind activity carried to excess, which point is further removed in some cases than in others, results in retardation of growth, even though no more serious consequences ensue. [Footnote 33: Educational Review, _op. cit._] [Footnote 34: Bryan, Addresses and Proceedings of the National Educational Association, 1897.] II.