THE EDUCATION OF THE NERVOUS SYSTEM. 345 



innervation of the skin in the former. For as growth 

 proceeds the skin increases in area more rapidly than 

 the nerves which supply it increase in number. In the 

 power of discrimination based on the condition of the 

 peripheral sense organs will probably be found the 

 anatomical condition controlling in large measure the 

 scale of human performance. Here we have in mind 

 the size of things made by man, ranging from the 

 minute and painfully detailed constructions to the 

 broad and carelessly general. Perhaps the extremes in 

 scales in painting and sculpture will best illustrate the 

 point. A Meissonier and Munkacsy could not inter- 

 change their styles at will, nor would the style of Michael 

 Angelo suit the needs of an engraver of gems. 



While in long periods fatigue in mental operations 

 can be demonstrated, in short periods the results are 

 not so clear, owing in part to the confusion caused by 

 the daily rhythms. Moreover, in the longer tests it is 

 difficult to give proper values to the quantitative reduc- 

 tion in the work done, and at the same time to the 

 decrease in accuracy, since the two do not run a parallel 

 course (Burgerstein, 1 Laser 2 ). Ebbinghaus 3 has made 

 the most elaborate tests on memory, and although his 

 experiments were undertaken on himself alone, they 

 suffice to show the easy onset of fatigue and the 

 enormous value of exercise alternating with even 

 lengthy periods of rest. Bolton,4 who studied in 

 scholars from eight to fifteen years of age the memory 

 span for a series of digits up to nine, found the length 

 of the span as well as the accuracy of its repro- 

 duction to increase with age. These improvements in 



1 Burgerstein, Trans. VIL^Internat. Cong. Hygiene and Demog., 

 London, 1891. 



- Laser, Zeitschrift f. Schulgcsundhcitspflege, vii., Jahrg., 1894. 



3 Ebbinghaus, Ueber das Gcdachtnis, Leipzig, 1885. 



4 Bolton, Am.Journ. of Psychol.^ 1892. 



