28 Thaddeus L. Bolton and Eleonora T. Miller 



work. We can not therefore attribute the gain here to the relief, 

 during the rest, from the generally unfavorable bodily conditions 

 which had arisen through the severity of the work before the 

 third rest. The hypothesis which seems most applicable is that, 

 as a result of exercise, the nerve centers and muscles were in a 

 state of incipient exhaustion, and that during the rest period 

 they built themselves up to the highest level of metabolic change 

 for which they have been prepared by the exercise. This is a 

 manifestation, apparently, of the advantages of not over-train- 

 ing, that is, the maximum performance of a muscle is to be 

 attained only after a suspension of practice for a few days. This 

 point will come up again. 



During the fourth period the work continued for nineteen 

 days. On the first eleven days only one record a day was taken 

 and on the remaining days two records a day. The left hand of 

 M. started out considerably better than the right and remained 

 ahead for eight days. The left then lost for a considerable time 

 while the right made steady and rapid gains during the whole 

 period. The left, however, began again to show great practice 

 gains when two records a day were taken up, and continued to 

 gain steadily and rapidly until the experiment was given up. 



Influence of practice by one hand upon that of the other. — 

 B. injured the right hand so that it was impossible to wear the 

 mask, and no records of any kind were taken for twenty-two 

 days. While the left hand had shown a loss during the third 

 series and none of the records were equal to the best in the sec- 

 ond series, the practice gain as shown by the records at the be- 

 ginning of the fourth series was surprisingly great, and from 

 that time on to the end of the experiment the practice increase 

 was uniform and considerable. The right hand began practice 

 again, and from the records it would appear that it had gained 

 almost equally with the left hand during the interval in which 

 the left only was exercised. In order to see how much gain has 

 actually taken place we must compare the average for the four 

 records of the first part of the second series with the first four 

 records taken after practice was resumed in the fourth. Before 

 the influence of a lack of inurement showed itself the average 

 for the normal records of the second period was 1602.4 and for 



106 



