DISCRIMINATION EXPERIMENT WITH WHITE RATS 



161 



Methods. — The boxes were placed upon the arc of a circle of 

 80 cm. radius near the end of a black-slate table of about a 

 meter width. The following diagram will show conditions: 



Figure 2. — Plan of apparatus. 1, 2. Food-box. Bo. Boards six inches wide 

 which were placed on edge so as to pen off the area used in experimentation. 



a, b. Chalk line along which boxes were shifted. -< indicates the position 



where the rat was placed and direction of the head. 



Boards were used to close off the rest of the table. The ex- 

 periment was carried on in a dark basement room and the black 

 boxes were on the side of the room and of the table away from 

 the light. Thus two dark objects against the dull background 

 of the walls rested upon the slate table. Above these were 

 the lights. The rats were kept in cages in the animal room and 

 brought in a small wire cage to the room where the experiments 

 were conducted. Before the rat was taken from the carrying 

 cage a bit of food (bread soaked in milk) was placed in a dish 

 in each box. A net was placed over the dish which was not to 

 be in the food box for the rat being tested. The food and net 

 were low in the dish and out of sight. This was to provide the 

 same sensory stimuli in all particulars except the one to be dis- 

 criminated. The light over the one box was started swinging 



