WHITE RAT AND THE MULTIPLE CHOICE METHOD 223 



oratory. Outbred females A and B and male D, all of the same 

 litter, were born February 11, 1915, and were about five months 

 old when they were first used, early in July. Inbred male J was 

 born March 1, and began work early in August when five months 

 of age. Inbred female C from another line was younger than 

 the others, being born March 27 and beginning work when about 

 three months of age. 



These five subjects were selected from nine rats which were 

 given preliminary training. They proved readier in forming 

 the food-association and in getting accustomed to the apparatus 

 than the other four, and it therefore seemed possible to bring 

 them to a more uniform state of preparation prior to the actual 

 experiments. 



There were, however, very noticeable individual differences 

 from the outset. A was rather timid, entering the compart- 

 ments cautiously and with hesitation. D worked rather slowly 

 and appeared in poor health from the start. B and C were ex- 

 tremely active and energetic, choosing successive doors with 

 great rapidity and running to the food-dish at full speed. 



The rats were not paired, but two or three of the same sex 



were caged together. 



APPARATUS 



The experiments were performed in a well lighted attic room 

 at the writer's home in Haverhill, Massachusetts. A ground 

 plan of the apparatus is shown in figure 1. It consisted of nine 

 similar compartments, C, C, etc. with a door at each end, — the 

 front door giving access to the reaction-chamber R and the rear 

 door to the back alley A. The compartments were placed equi- 

 distant from the door of the entrance box E, along the arc of 

 a quadrant of a circle. 



The various doors, of sheet brass, were arranged to slide ver- 

 tically and were operated from the experimenter's table by 

 weighted strings passing through screw eyes above the doors. 

 Those doors leading from the reaction-chamber into the nine 

 compartments were arranged to remain 3-16 of an inch from the 

 floor when closed, to avoid pinching the animal's tail. The 

 entire apparatus was covered with wire netting and the floor 

 was sprinkled with a light layer of sawdust. 



From the reaction chamber the animal could enter one of the 

 nine compartments, pass into the back alley, thence to the side 



