Yerkes, Inhibition and Reinfoixemejit. 131 



minute, was so arranged that at a certain point it closed an 

 electric circuit in which I had placed a magnet. This magnet 

 attracted a steel arm at the end of which a disc of red card- 

 broad 12 mm. in diameter was suspended. With the making of 

 the circuit the steel arm was drawn downward suddenly and the 

 red disc, by reason of the vibrations of the arm moved rapidly 

 back and forth in front of a window in the reaction-box. In 

 this way the moving object was exposed to view about 10 cm. 

 to the right and 3 cm. in front of the right eye of the frog. 

 The revolving disc, a fraction of a second later, completed the 

 electric stimulus circuit. Thus both stimuli were given auto- 

 matically, at such an interval apart as the experimenter desired. 

 In the two series of results now to be described the intervals 

 were o. i and o. 5 second respectively. 



These series consisted of 25 pairs of reactions each, with 

 two animals. The results of the series are presented separately 

 because the experiments wliich constitute them were separated 

 by a period of three weeks, during which time the conditions 

 of the frogs changed noticeably ; they became less active and 

 less sensitive to stimuli. 



The lower half of Table III contains a simple statement 

 of the results of these series. It is to be noted that these re- 

 sults agree fully with those of the preliminary series. The vis- 

 ual stimulus of a moving red disc, given o. i second before a 2 cell 

 electric stimulns, reinforces the electric reaction, i. e. , it shortens the 

 time of reaction. The same visual stimidus given o.j seconds be- 

 fore tends to inhibit the electric reaction, i. e. , it lengthens the time 

 of reaction. 



Table IV contains the various values determined for the 

 results of these series. The general averages for the results of 

 the Preliminary Series and those of Series I are as follows : 



