16 JOSEPH U. YARB ROUGH 



senting the light may be seen in Fig. 3. Directly above the long 

 central runway and in contact with the frame of the glass cover 

 of the box a piece of soft pine i" x 2" - 4' is attached, and to 

 it is affixed two lamps connected in parallel. The first lamp is 18" 

 from the end of the box; the second is 22" nearer the food-box. 

 National Mazda 100 Watt lamps are connected on a 115 Volt 

 circuit. In order to direct the light upon the zigzag pathways 

 a reflector is suspended directly over the lights and so adjusted 

 that the light falls on these runways only. With proper electric 

 connections the timing apparatus enables us to present sound and 

 light in a certain known temporal relation, just as the buzzer 

 and pain were previously presented. 



The method of procedure may be described as follows : The 

 animal to be tested is put through the door D from the food-box 

 F into the central runway C. He is required to go up to point 

 O and turn either to the left or to the right and return through 

 the zigzag pathway X or Y, through the door Di or D2, and 

 through D3 into the food-box F where he is given food. It is 

 of little interest in these experiments whether the animal turns 

 to the one side or the other, or to one side altogether, for the 

 problem is in no way affected by the alley chosen or by position 

 habit. The alley chosen in no way determines what is to follow. 

 Seven times out of ten trials the animal is given an electric 

 shock in the return zigzag runway; no shock is given in the 

 three remaining trials. This shock may be given at any point 

 along the runway, lasts for a period of one-half second, and is 

 given only once during the trial. The problem here is to learn 

 to turn around for pain or to go on in case no pain is given. 

 If pain is given and the animal does not turn around but goes 

 on toward the food-box he finds the door at the end of the alley 

 closed. Thus, for example, if the door is D2 he must, to gain 

 entrance to the food box, run back through the zigzag alley Y, 

 pass the point O, and approach through the alley X and the door 

 Di. When no pain is given the door of the alley selected is 

 always open and the animal enters the food-box direct. The 

 problem here may, therefore, be thought of as an association 



