6 STELLA B. VINCENT 



the blocking of pathway "C" at the farther end to make it a 

 blind alley instead of a longer way around (Fig. 1). The essen- 

 tial difference, however, was the fact that the true pathways 

 and the blind alleys were made to differ as far as possible in 

 brightness. Black cardboard lined and covered the one and a 

 very white paper lined the other. In the later experiments 

 black and white enamel paint was used on the floor and sides 

 while black cardboard covered the top of the black pathway. 



The problem box for the discrimination tests was a paste- 

 board box 12' x 12' x 9', with round tubes inserted at the floor 

 level in opposite sides. One tube was white, with white oiled 

 paper pasted in the upper third to increase the brightness, the 

 other tube was black. The tubes were not straight but were 

 bent in the middle at right angles to prevent any entering light 

 from the end of the open tube from giving a clue. Only the 

 tube of the brightness for which the animal was being trained 

 remained open at the end. The box was turned in an irregular 

 order to prevent choice by position. 



The only stimulus to the activity was the reward of food at 

 the completion of a successful run in the maze or the choice of 

 the right exit in the problem box. Five animals usually consti- 

 tuted a group. 



Some records were first made upon the maze as it originally 

 stood with walls and floor of unpainted pine. A group of un- 

 trained rats was given 50 trials covering a period of 18 days. 

 These rats were then taken over to the problem box where they 

 were given 50 trials. Then another group of rats which had 

 previously been given 50 trials on the problem box was put in 

 the maze for 50 trials. Ten trials a day were given in the prob- 

 lem box, but on the maze only 3. These records are referred to 

 as the normal records and furnish the standard for comparison. 



The maze was then made black and white, the true path black 

 (see dotted line, Fig. 1) and the blind alleys white. Two other 

 groups of rats learned both it and the problem box in alternation 

 as above. This maze is sometimes spoken of as the black maze. 



The third change consisted in making the true path white 

 and the cul de sacs black and using two new groups of animals 

 in the manner described above. This maze is occasionally re- 

 ferred to as the white maze. 



In brief the experiments upon which this discussion is based 

 are as follows: 



