114 EXPERIMENTAL PHYSIOLOGY 



obtained by forcibly bending the foot at the ankle, can also be well 

 observed in such a preparation. 



Reaction time in man. The reaction time in man may be deter- 

 mined by an arrangement of electric signals, but is done more simply 

 by Waller's apparatus (Fig. 86). This consists of two wooden levers 

 lying across a piece of india-rubber tube one end of which is 

 closed ; the other is connected with a tambour which writes upon a 

 drum the speed of which should be moderate. A screen hides the 



FIG. 86. Waller's apparatus for reaction time, a, Rubber tube closed at one 

 end and at the other connected by b with a tambour (not shown) ; c, c', d, d', 

 levers (with coloured patches) hinged near c', cT, and resting on the rubber 

 tube, a ; e, wooden screen, (a should be placed on the other side of the 

 screen. ) 



movements of the experimenter from the person experimented on, 

 who sits at the table with one finger resting lightly on the 

 extremity of one of the levers. He is to respond by pressing the 

 lever the instant he (1) feels a movement of that lever, his eyes 

 being shut; (2) hears a tap on the second lever; (3) sees a move- 

 ment which is imparted to the second lever by the experimenter, 

 who presses it down on the other side of the screen. In each case 

 two marks are recorded upon the abscissa : one being that which 

 is made by the experimenter in imparting the stimulus, and the 

 other that made by the observed person in responding. The interval 

 between the two marks, which can be accurately measured by the aid 



