NERVOUS SYSTEM. 



CHAPTER XXX. 

 KEACTION TIME. 



THE time which elapses between the application of a given stimulus 

 and the prearranged response of the subject to that stimulus is known 

 as the reaction time. It is obviously more complex than a reflex 

 action; this will be readily understood from a consideration of the 

 following determination of the reaction time. 



Mil Ik 



FIG. 236. Diagram of the apparatus for the determination of reaction time. 



The diagram 236 shows W. Gr. Smith's reaction time apparatus as 

 modified by Colls. The electro-magnetic tuning-fork, T, with 100 

 vibrations per second, is connected with two Daniell cells and with the 

 chronograph C. By means of either of the two Du Bois keys, K x 

 and K 2 , the chronograph can be short circuited. The key Kj is closed 

 and K 2 is open ; the tuning-fork is set vibrating, but does not 

 affect the chronograph. The subject, whose reaction time is to be 

 determined, is told to listen for the sound of the opening of 

 the key K x and to close the key K 2 directly he Clears the sound. 

 When the key K x is opened the chronograph vibrates in unison 

 with the tuning-fork and the vibrations are recorded upon a 



