BEHAVIOR OF STOCK AND INBRED ALBINO RATS 279 



which the time records show was not the case. A combination 

 of time and error or time and distance curves apparently gives 

 the most adequate representation of the facts obtained from 

 these stock and inbred rats. 



2. DISCRIMINATION METHOD 



When the inbred rats were first received from the Wistar 

 Institute, a few preliminary experiments were made by Pro- 

 fessor Yerkes and two students, using the brightness discrimi- 

 nation method and twelve animals, six stock and six inbred, 

 three males and three females each. The results of these ex- 

 periments are given separately from the writer's, which were 

 conducted a year later at the Franklin field-station. The former 

 animals are designated Group 1, the latter, Group 2. The 

 apparatus was exactly the same for all. Artificial light was used 

 for the earlier, and daylight for the later experiments. The 

 animals of the first group -were from 46-55 days old when the 

 experiments were begun; those of the second group were eight 

 of the nine young rats which had recently been tested in the 

 short maze. As soon as the maze experiments were finished 

 the rats were sent from Cambridge to Franklin and experi- 

 ments were begun June 17. The rats were at this time 75 

 days old. One of the stock rats met with an accident soon 

 after the beginning of the experiments so that the results are 

 given for four stock and four inbred rats, two males and two 

 females each. 



The apparatus used was in essentials the Yerkes discrimi- 

 nation box. 10 It consisted of a box 52 cm. long by 40 cm. wide 

 by 18.5 cm. deep. Attached to this at one end was a smaller 

 food' box 16 cm. by 14 cm. by 18.5 cm., having a hinged wooden 

 cover, with a small hole in the centre. An animal to be tested 

 was allowed to enter from the food box, by means of a sliding 

 door, a narrow passage. This led through a door of wire mesh, 

 swinging inward from the top, to a chamber 15.4 cm. by 18 cm. 

 From this led two pathways or discrimination boxes, 20 cm. by 

 8.5 cm., differentiated only by the amount of light entering 

 them. These communicated by openings in the side walls at 

 the rear with passageways by means of which return was effected 

 to rooms adjoining the entrance passage from which the animal 



10 Yerkes, R. M. The dancing mouse. New York, 1908, p. 92. 



