THE CENTRAL NERVOUS SYSTEM 383 



2). Let stimulating electrodes pass from the 

 secondary coil (bridge up) to the tongue of the 

 subject. Let the subject hold one key .closed un- 

 til he feels the stimulus on the tongue. 



Direct the subject to shut his eyes. Let the ob- 

 server start the tuning fork, spin the drum, and 

 stimulate the subject by completing the primary 

 circuit. The instant the subject perceives the 

 stimulus, he will break the circuit by releasing 

 his key. By means of the tuning fork curve 

 determine the interval between stimulation and 

 response. This interval is the reaction time plus 

 the errors of observation ; for example, the latent 

 period of the electromagnetic signal. Eepeat the 

 experiment three times and take the mean of the 

 results. 



In the laboratory note-book make a list of the 

 links in the chain between stimulus and re- 

 sponse, and state as far as possible the errors of 

 observation. 



Reaction Time with Choice. Connect the 

 side cups of a pole-changer (without cross wires) 

 to the posts of the secondary coil. Connect one 

 pair of end cups with the usual stimulating elec- 

 trodes, the other pair with large brass electrodes 

 covered with wet cotton. Let the ordinary elec- 

 trodes touch the forehead, the other pair the hand 

 of the subject. The other connections should re- 



