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POPULAR SCIENCE MONTHLY. 



second set of tracings, gained from a girl, E. EL, 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 mus- 



cles, 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 ad- 

 verted to, and who indicated here, as in the other tests, that his morn- 

 ing's duties had had no serious effect upon his nervous energies. 



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 



