DOCKERAY : PHYSICAL FATIGUE AND MENTAL EFFICIENCY. 201 



first group he gave difficult lessons; to the second group, easy 

 lessons ; and to the third group, rest for the same period. The 

 tests correlated with the groups. Thorndike (38) repeated 

 similar tests, but found no correlation. 



Reaction times and the spatial threshold as tests of fatigue 

 have been used, but the greatest fault with either method is 

 the great difficulty in determining what function is measured. 

 Considerable dispute has arisen as to whether change in re- 

 action time is a function of a change in the sensory or motor 

 process or in attention. Scripture (34) found that "fatigue in 

 reaction time increases with the complexity of the adjustments 

 required for perceiving the stimulus. There is least fatigue 

 when only an act of attention is involved." (p. 19.) Milroy 

 (27) used one subject on continuous reactions, and found 

 longer reaction times in the last half of the interval, but 

 changing the sense organ did not interfere with the retarda- 

 tion. 



The most careful study of physical fatigue by means of re- 

 action times was done by Bettman (1). Unfortunately he 

 was the only subject for the experiments. He performed the 

 experiments, with the aid of an assistant, during vacation, 

 under as uniform conditions, so far as diet, sleep, etc., are 

 concerned, as is possible. The tests consisted of fifty choice 

 reactions before and three hundred choice reactions imme- 

 diately following the work or the rest periods. He either 

 walked two hours, added one hour, or rested one hour. The 

 results showed an increase in reaction time after mental work 

 and a decrease after physical work, though the greater num- 

 ber of false reactions in the latter case is considered as evidence 

 of decreased mental activity after physical work also. He also 

 employed in place of the three hundred choice reactions a com- 

 bination of fifty choice reactions, a half hour of adding and a 

 half hour learning nonsense syllables. In these tests, also, he 

 found a decrease in mental activity after either form of work. 



The sesthesiometer method has been more widely used as a 

 test of fatigue, but is open to some of the same objections as 

 the reactions test. The chief fault, however, is the brevity 

 of the test as frequently used. Griesbach (13), for example, 

 was able to examine six to ten subjects in ten minutes. Any 

 one familiar with the two-point threshold experiment would 

 expect variations that would obscure the real character of the 



