170 BINNIE D. PEARCE 



behind the main apparatus. Between the boxes was an aper- 

 ture, O, covered with a piece of clear glass and a variable number 

 of sheets of typewriter paper (Post Office bond). These varia- 

 tions and the c.ps. employed will be given below. The light 

 was controlled with a switch at S. The rat was expected to 

 react to the presence or absence of light by turning to the left 

 or the right as the conditions of the experiment required and 

 as will be detailed later. When the reaction to the stimulus 

 was correct, the animal escaped through an open alley (A) to 

 food at F ; when incorrect, an electric shock was given "by means 

 of the wires marked E and E' and a free exit was blocked by 

 means of a movable end-stop, placed in the alley A'. At each 

 trial the rat was introduced directly into the discrimination box 

 through an opening at F and the stimulus was presented im- 

 mediately. Punishment and reward was used throughout the 

 test. The following series of presentations were used, 10 trials 

 daily : 



llrlrrlrlr 



r 1 1 r r r 1 1 r 1 



r r 1 r 1 1 r 1 1 r 



lrrlrrlrll 



EXPERIMENTAL RESULTS 

 I 



The present experiment was begun with four untrained rats 

 (adults). Later four new untrained rats were added. Of these 

 one (No. 10) was 42 days old; one (No. 13), 37; and two (Nos. 

 14 and 15) 68 days old. Unless otherwise stated the results 

 given are for all eight rats. 



On each of 3 consecutive days the animals were allowed to 

 make 5 preliminary runs in the box, the object being to acquaint 

 them with the apparatus and to accustom them to receiving 

 their food at F. These trials were given without light stimulus, 

 punishment or end-stops, save that the latter were used where 

 necessary to prevent the appearance of position habits. 



In the regular test, habit No. 1, a correct response required 

 the rat to turn through the right hand passage when light was 

 present and through the left hand passage when the light was 

 absent. The light used in this first test was a mazda 32 c.p:; 



