Yerkes, Inliihition and Reinforcement. 125 



one second) before the giving of the electric stimulus, (4) the 

 effect of visual stimulation by a moving red disc, shown in one 

 series of experiments o. i", and in another o. 5" before and until 

 the electric stimulus was given. 



In all cases the reaction-time to electric stimulation of the 

 skin was studied with special attention to the influence of other 

 stimuli which were given in definite temporal relation to the elec- 

 tric stimulus. The general method of the investigation was the 

 same as that described in my earlier paper (p. 601). A Hipp 

 chronoscope, controlled by a Cattell's falling screen, served as 

 a time measuring apparatus. The other essentials of the appa- 

 ratus were a reaction-box, and devices for giving the stimuli 

 and indicating the reaction. On the bottom of the reaction-box 

 a series of wires were so placed that an electric stimulus could 

 be given to the frog resting upon them by the closing of a key 

 in the hands of the experimenter. In preparation for each ex- 

 periment the frog was placed upon these open circuit wires in 

 such a position that the weight of its body pressed upon a deli- 

 cate spring in the floor of the box, thus causing the chronoscope 

 circuit to be completed. The forward jump of the frog in re- 

 sponse to stimulation caused the breaking of this circuit by the 

 release of the spring upon which the animal rested. When all 

 was in readiness for an experiment the chronoscope was started, 

 and a key closed which simultaneously gave an electric stimulus 

 to the frog and completed a circuit which caused the chrono- 

 scope record to begin. The stimulus consisted of a current 

 from one or more "Mesco" dry batteries. The motor reaction 

 of the frog broke the chronoscope circuit, thus causing the 

 chronoscope record to stop. It was then possible for the ex- 

 perimenter to read from the dials of the chronoscope the time, 

 in thousandths of seconds, intervening between stimulus and 

 reaction (reaction-time). In case of additional stimuli in con- 

 nection with the electric, various simple devices were intro- 

 duced to meet the demands of the experiments. These will be 

 described in connection with the statement of results in each 

 case. 



