July 29, 1898.] 



SCIENCE. 



133 



It would be difficult to select a topic in the 

 field of psychology that would enlist a wider 

 interest than that of mental fatigue. It is one 

 of the most characteristic of the ills that flesh, 

 or at all events civilized flesh, is heir to. From 

 the school boy to the professor, in all profes- 

 sions and in business, the cry is overwork, ex- 

 haustion and fatigue. The well known tired 

 feeling is altogether too familiar, particularly 

 in newer civilizations and in communities in 

 which the push and drive of commercial ambi- 

 tion set the pace for an equally exhausting 

 social and intellectual competition. As a ques- 

 tion of practical hygiene the avoidance of undue 

 fatigue is of the highest importance ; and here, 

 as elsewhere, the only certain path to relief is 

 the one that leads through a systematic study 

 of the nature of the normal and abnormal pro- 

 cesses concerned. The physiology and psychol- 

 ogy of fatigue must be minutely and success- 

 fully investigated before the practical applica- . 

 tions can be made to the routine of the school 

 room or the most economical division of labor 

 for the intellectual worker. In a matter of 

 such fundamental and familiar import there is, 

 of course, a considerable accumulation of wis- 

 dom, which, however vague or ill arranged, 

 must not be altogether despised. It is, unfor- 

 tunately, true that in many emergencies of life 

 our actions cannot be guided, even if we are 

 ready to guide them, by scientifically established 

 principles and logically vei-ified inductions. 

 Particularly in such complex matters as psy- 

 chology must take into account is there the 

 greatest necessity for discernment and caution 

 in applying knowledge to practice. Individual 

 diflferences and circumstantial details often pro- 

 foundly aflfect deductions ; for it is equally true 

 that one man's meat is another man's poison, 

 and that one man's work is another man's play. 

 These considerations are presented to imply not 

 that the management of intellectual eflbrt and 

 the avoidance of fatigue cannot be directed by 

 scientific principles, but rather by mother wit, 

 but only that the illumination of this field of 

 inquiry is a difficult and slow process. None 

 the less we can dispel the total darkness that 

 hangs over the region and here and there get 

 up a modest searchlight that may reveal the 

 more intimate nature of a few limited areas. 



The work of Messrs. Binet and Henri, though 

 not the first work on fatigue, is the first work 

 on mental fatigue, and the first attempt to 

 prepare a compendium of our knowledge 

 regarding the general topic. If the net 

 outcome seems meagre the above considera- 

 tions regarding the difficulties and newness 

 of the inquiry may be urged in excuse. It 

 should also be borne in mind that the removal 

 of misconceptions and the elaboration of a 

 method in themselves form a considerable ad- 

 vain ce. 



The investigations regarding mental fatigue 

 naturally fall into two divisions : first, the effect 

 of intellectual effort upon .physiological func- 

 tions ; and second, their efiect upon psycholog- 

 ical activities. The establishment of the gen- 

 eral principle that mental processes are corre- 

 lated with cerebral functions, which in turn 

 depend upon the integrity of a wholesome 

 blood supply, prepares us for the conclusion 

 that all intellectual effort modifies, however 

 slightly, the physiological status of the moment. 

 The ingenious demonstrations of Mosso and 

 others have revealed the marvellous delicacy 

 of this psycho-physical interdependence, that 

 seems to be limited only by the sensitiveness of 

 our devices for detecting it. More directly, 

 Hodge has shown the effects of more or less 

 prolonged fatigue upon nerve cells, so that our 

 conception of a tired nerve cell is no longer 

 purely a matter of hypothesis. There is, of 

 course, no definite point at which work passes 

 into fatigue ; the effects of fatigue are the 

 effects of continued activity, the intensity and 

 even the kind of effects depending upon the 

 prolongation of the effort. There are also the 

 accompanying subjective feelings of fatigue, 

 but these have not been made part of experi- 

 mental investigations. 



The first group of problems in such investi- 

 gation relates to the selection of typical forms 

 of mental effort and the technique by which 

 their efiect upon physiological functions may 

 best be noted. Counting the number of letters 

 in a printed passage, writing to dictation at a 

 maximum speed, reading aloud, numerical cal- 

 culations performed mentally, committing num- 

 bers or syllables to memory, have all been em- 

 ployed. The main desiderata for the most 



