118 APPENDIX I. 



emanating from neighbouring roots, but of very 

 unequal length. The person experimented on is 

 desired, as soon as he becomes aware of the shock, 

 or sensation-signal, as it may be termed, to answer it 

 by another signal, volition-signal, which generally 

 consists in making or breaking a circuit at the 

 instant when the sensation-signal is given ; and 

 means are provided for measuring the time, that we 

 shall designate by T, which elapses between the two 

 signals. The time T comprises, firstly, the time 

 required for the transmission of sensation to the 

 brain for its perception there for volition for 

 the transmission of volition to the muscles for 

 muscular contraction; secondly, T comprises the 

 time lost in the purely mechanical and physical 

 process of signaling. This last time, of course, 

 depends upon the experimental method employed, 

 and by suitable arrangement may even be reduced 

 to nothing. Now, should the value of T, when the 

 more distant place on the skin is stimulated, always, 

 and by nearly the same amount, exceed its value 

 when the nearer place is stimulated, then, as every- 

 thing else in both experiments remains the same, 

 the difference of time must obviously depend upon 

 the unequal distance which in both cases the 

 nervous agent has to travel from the place stimulated 

 to the brain. 



This scheme also, in the main, was suggested by 

 Professor Helmholtz, as early as 1850 ;* the first 

 correct results, however, were thus arrived at eleven 



* KonigsbergerNalurwissenschaftliche Unterhaltungen. Bd. ii., 

 Hft. ii. 1851. S. 169. 



