THE 



POPULAR SCIENCE 

 MONTHLY. 



AUGUST, 1882. 



THE PHYSIOLOGY OF EXEECISE. 



By EMIL DU BOIS-REYMOND. 



II. 



BETWEEN the external sensation and the internal perception 

 stands the time-sense, adapted to the distinction and estimation 

 of the succession ; it is really a grosser hearing and sight, for the 

 cochlea and retina do nothing more than distinguish the more or less 

 rapid succession of impressions. The time-sense is susceptible of 

 a high degree of training, as may be learned from intercourse with 

 astronomers and watch-makers. The later chronoscopy has warranted 

 the possibility of determining the educability of the nervous system to 

 a punctual obedience. In the experiments which Herr Donders first 

 made tentatively, the mean of the time which the same observer re- 

 quired to execute a determined movement in accordance with some 

 signal which he saw, heard, or perceived, sunk from day to day to a 

 limit which was soon reached. The result was the same in a small 

 degree which the drill-master enjoys in a large degree, when to his 

 command a single sound responds, hardly longer protracted than to 

 twice the difference in the time required for the sound-wave to pass 

 from him to the nearest and to the farthest man. 



Finally, the internal sense also, which has already entered into our 

 considerations, is susceptible of exercise. Before all, the memory is 

 strengthened by practice to a certain degree, and according to its em- 

 ployment in different directions. It may be recorded here that, as I 

 have heard Schleiden relate, Robert Brown was able to distinguish 

 twenty-five thousand species, Kunth only twenty thousand species of 

 plants ; and, if Kunth undertook to impress more than that number 



* An address at the anniversary of the Institute for Military Surgeons, Berlin, August 

 2, 1881. 



vol. xxi. 28 



