O'SHEA — ASPECTS OF MENTAL ECONOMY. 51 



tion they cannot at the same time be employed in another. In 

 amplification of this axiom attention may be called to what 

 every one has doubtless observed, that when one is engaged in 

 hard muscular labor, he is less keen and vigorous in his men- 

 tal processes; and when he is under great emotional excite- 

 ment he cannot accomplish so much intellectually. Again, 

 when the vitality of the system is dissipated in repairing the 

 ravages of disease, the individual is unable to command so 

 great force in the accomplishment of either physical or mental 

 tasks. This conception, which is endorsed by experience and 

 substantiated by physiological and psychological science, is a 

 most important one as it relates to the ordering of the daily 

 life of any person and especially that of a student. To but 

 indicate its bearings here, it may be pointed out that the vigor, 

 efficiency, and spontaneity of either physical or mental activi- 

 ties in the business, social, and educational world depend in 

 some degree upon the amount of nervous capital one has on 

 deposit in the central nervous mechanism. Abundant research 

 has proven, it seems, that cerebral depletion (and depletion 

 is, of course, a relative term in respect of the readiness with 

 which it ensues in different people) reduces the force of mus- 

 cular effort, renders attention less concentrated, resulting in 

 a gradual obscuration of mental vision, and estranges the emo- 

 tional nature, begetting a general condition of disphoria and 

 apprehensiveness, and removing restraints upon anti-social im- 

 pulses, as jealousy, anger, irritability, and similar traits of a 

 low order of development. 



Mosso, 1 Maggiora, 2 Lombard, 3 Bryan, 4 Kraeplin, 5 and others 

 have shown that in a condition of fatigue muscular activity 

 is lessened in force and reduced in rapidity; and this 



1 Ueber die Gesetze der Ermiidung, Archiv. fiir Phys. (DuBois Reymond.) 

 Hefts, I and II, 1890. 



J Ueber die Gesetze der Erniiidung. Untersuchungen an Muskeln des Menschen. 

 Archiv. fiir Anat. und Phys. (DuBois Reymond.) Physiologie, 1890, pp. 89-243. 



3 Some of the Influences which Affect the Power of Voluntary Muscular Con- 

 tractions. Journal of Physiolgy, vol. XIII, pp. 1 and 58. 



4 The Development of Voluntary Motor Ability, Am. Jour, of Psych., 5, p. 123 

 -et seq. 



6 A Measure of Mental Capacity. Popular Science Monthly, vol. 49, p. 756. 



