238 KANSAS UNIVERSITY SCIENCE BULLETIN. 



CONCLUSIONS. 



One of the common fallacies in the study of fatigue, Squires 

 (36) has pointed out, is to consider it as a simple phenomenon. 

 It is true we may isolate a muscle and produce a fatigue that 

 is relatively simple, but in the usual conditions of what we 

 term fatigue we are dealing with a complexity that is difficult 

 to analyze. If we accept Thorndike's definition of fatigue as 

 "that diminution of efficiency which rest will cure" the prob- 

 lem seems simplified. But we still have to reckon with the 

 physiological and mental factors that bring about this diminu- 

 tion of efficiency, and their relative influence is not always 

 so easily determined. 



We find that the effect of physical fatigue upon mental 

 efficiency, as expressed by addition and multiplication, is very 

 irregular. A subject may do better after a work period than 

 after rest, or he may show an increase in speed and a decrease 

 in accuracy. This agrees with the results of Ebbinghaus (10) 

 and those of Heck (15) in their experiments on mental fatigue 

 in school children. Again, the subject may improve after 

 physical work in proportion to the amount of work done; 

 thus, Ba. failed after rest, did less poorly after running 

 eighteen laps, and improved after twenty-seven and thirty- 

 six laps. The sounder and association tests, on the other 

 hand, present more uniform results, and, in most cases, show 

 a diminished efficiency after physical work. 



Two theories present themselves as explanations of these 

 results. (1) It may be that the fatigue products generated by 

 the physical work, either in the motor neurones or in the 

 muscles, spread through the circulation to the association cen- 

 ters and cause directly a diminution in the efficiency of the 

 association processes; or, (2) it may be that the sensations 

 that accompany fatigue serve as distractions and thus cause 

 a decreased attention. The former view is partially borne 

 out by the results. As in Ranke's (33) experiments the per- 

 fusion of an isolated muscle with a weak solution of sarcolactic 

 acid caused a heightened excitability, so it is possible that a 

 certain amount of physical work would produce a sufficient 

 amount of fatigue substance to cause increased mental ac- 

 tivity ; a greater amount of this fatigue substance would cause 

 a decreased mental activity. Ba.'s results (Table lib) would 



