LESSON XXXV 



THE NERVOUS SYSTEM (Concluded) 

 REACTION TIME 



1. Reaction to Touch. Arrange the electric apparatus for stimula- 

 tion with single induction shocks. Insert a signal and two simple keys 

 in the primary circuit of an induction apparatus, and connect a pair 

 of platinum electrodes with the secondary coil. Arrange to record the 

 movements of the signal. Add a tuning-fork. The latter should be 

 fastened to a separate stand and be allowed to record from left to right, 

 i. e., against the direction of rotation of the drum of the kymograph. 

 Let the subject hold the electrodes against his tongue with his left hand, 

 while his right hand grasps the handle of one of the two keys. Let the 

 observer then spin the drum and close the other key. As soon as the 

 subject feels the make shock, let him break the current by opening 

 his key. Draw ordinates to the curves and determine the time which 

 has elapsed between the make and the break of the current. Repeat 

 this experiment several times and ascertain the average reaction time. 



FIG. 99. REACTION TO TOUCH. 



Record of signal below that of tuning-fork (^ sec.). S, Moment of stimulation; R, mo- 

 ment of reaction. 



Repeat this experiment with a stronger stimulus. What relation- 

 ship exists between the strength of the stimulus arid the length of the 

 reaction time? 



2. Reaction to Light. Arrange 5 dry cells in series, their total 

 strength amounting to about 7 volts. Connect these cells with a siriall 

 incandescent lamp (5 or 6 volts), a signal, and two simple keys. Ar- 

 range to register the movements of the signal above the record of a 

 tuning-fork vibrating in hundred ths of seconds. Let the subject hold 

 the bridge of one key in the position of closure. Shield the other key 

 and apparatus from the subject by a large cardboard. Let the observer 

 spin the drum and suddenly light the lamp by closing the bridge of the 

 second key. The subject should open his key as soon as he perceives 

 the light. Determine the average reaction time of several tests of this 

 kind. 



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