DISTRIBUTION OF EFFORT IX LEARNING IN WHITE RAT 47 



There remain two possible explanations why one trial a day 

 or at greater intervals is the most economical. First, it may 

 be supposed in opposition to the above that several trials a 

 day might produce fatigue; secondly, that they might produce 

 too pronounced metabolic changes. In regard to fatigue no ob- 

 jective manifestations of its presence were noticeable; for there 

 were no differences in the responses evoked at each trial, when 

 several were given, that would indicate that the last trial was 

 performed with more difficulty than the first. The rats were 

 active throughout all trials given for one day. Moreover, the 

 last trial required often less time for the solution of the prob- 

 lem than the first. This can be seen in Tables IX and X, 

 where daily records for three days are given of the three 

 and five trial groups with one problem and with three abreast. 

 The shortest trial on any day is often shown to be the last trial 

 given on that day. Even when three problems were given 

 abreast with five trials for each problem — a total of fifteen trials 

 a day — the last few trials of the fifteen were oftentimes per- 

 formed with a similar facility. The short break in this case in 

 passing from one of the problems to the other can scarcely 

 be counted as periods of rest. 



The second explanation that several trials cause too active 

 metabolic changes is as near the truth as can be reached at 

 the present time. It is possible that with one trial a da}^ or 

 at greater intervals just sufficient transformation of energy 

 occurs to make every trial physiologically effective, whereas, 

 when several trials are given concurrently, there is a too rapid 

 and extensive transformation of energy. The necessary anabolic 

 changes after each trial are not permitted to take place before 

 the other trials follow, and, as a result, katabolic changes increase 

 to such an extent that the effectiveness of each trial is impos- 

 sible to establish. Probably the first of several trials is physio- 

 logically the most effective, the others being proportionally less 

 so. To produce a change in the animal so that learning will 

 be most economical, one trial daily or at greater intervals is 

 the best. 



