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SCIENCE. 



[N. S. Vol. VIII. No. 187. 



suitable experimental mental effort is one that 

 shall involve a minimum of motor expression; 

 that shall, too, as nearly as possible, involve the 

 same processes when performed by different 

 persons; that shall involve continuous but not 

 too severe concentration, and that shall yield 

 results by which the dui-ation and the correct- 

 ness of the task performed can be measured. 

 No one of the above processes answers all of 

 the requirements — and they are not the only 

 ones — but on the whole the authors prefer the 

 dictation and regard simple calculations as 

 highly appropriate. One further general fact 

 must be taken into account. In repeatedly per- 

 forming the same mental task we become more 

 proficient and do it more rapidly and better. 

 Fatigue would tend to lengthen mental pro- 

 cesses and introduce error. Hence the effect of 

 practice tends to counteract and disguise the 

 .effects of fatigue ; still it would remain true 

 that the most fatiguing type of effort would 

 show a less rapid increase of efficiency with 

 practice than lighter occupations. Neglecting 

 for the moment these and other difiiculties, we 

 may briefly review the established results re- 

 garding the effect of certain typical forms of 

 intellectual effort upon physiological and psy- 

 chological functions. 



It appears that intellectual effort at first 

 quickens the heart beat, but later (after 30 

 minutes or more) slackens it ; at the same time 

 the pressure of the blood is increased ; more 

 blood flows to the brain, and the character of 

 the pulse curve is affected. Likewise the res- 

 piration is quickened, but the amplitude of 

 each inhalation is diminished and the amount 

 of carbonic acid given off and of oxygen absorbed 

 is increased, while for any considerable mental 

 effort the bodilj' temperature becomes higher. 

 It likewise appears that the effects of prolonged 

 effort are frequently of an opposite character 

 to those of a brief, even if violent, effort, 

 and that individual differences are significant. 

 Moreover, most of these results are quantita- 

 tive in character, and by far the largest portion 

 of the first part of the volume (in itself over 

 200 pages) is devoted to a technical account of 

 the equipment by which such quantitative re- 

 sults may be secured. 



A particularly important relation is that be- 



tween intellectual effort and muscular effort. 

 A brief mental exertion (15 minutes or less) 

 seems to increase the momentarily available 

 muscular energy as measured by the dyna- 

 mometer, but a longer mental exertion distinctly 

 decreases it, and particularly does it decrease the 

 total capacity of muscular work as measured by 

 the Ergograph. Emotional excitement in con- 

 nection with intellectual work may postpone 

 the muscular enfeeblement and continue for a 

 longer period the increase of muscular energy 

 which appears to accompany brief mental exer- 

 tions. Furthermore, the effect of longer and 

 shorter periods of rest may be measured by 

 their restoration of the total working energy as 

 compared with the normal. In some of Mosso's 

 subjects this tendency of mental work to de- 

 plete the muscular energy is most striking ; 

 and the Ergographic curves written by a pro- 

 fessor on three successive days of holding oral 

 examinations of candidates for a degree reveal 

 a progressive muscular exhaustion, which in 

 turn gives place to a gradual recuperation after 

 one or more days of rest. Evidence of this 

 character leads Professor Mosso to hold that 

 physical exercise is not a proper relaxation from 

 mental effort ; absolute rest of mind and body 

 is more desirable and effective. In this con- 

 nection, as well as elsewhere, it is important to 

 emphasize the difficulty of establishing a nor- 

 mal by which deviations caused by mental ex- 

 ertion or other influences may be measured ; for 

 there are larger and smaller fluctuations of all 

 kinds. The morning and the evening, before 

 and after meals, or sleep, the summer and 

 winter, age, sex and temperament, all intro- 

 duce complications which can only be eliminated 

 by prolonged and logically conducted observa- 

 tions. 



Before proceeding to the more strictly psy- 

 chological studies attention may be drawn to 

 two interesting fatigue curves, which the au- 

 thors have found in their observations. The first 

 relates to the consumption of bread in certain 

 French boarding schools for the different 

 months of the year, it being understood that 

 bread is supplied ad libitum. It appears that 

 in the months following the vacations most 

 bread is consumed, the amount decreasing with 

 fair regularity until the minimum is reached in 



