334 ^Journal of Comparative Neurology atid Psychology. 



It was important in connection with the experiments to make 

 the conditions such that the rat would make the greatest effort of 

 which it was capable to perform the required act. 



To get this result it was found necessary to fulfill three conditions . 

 In the first place the animal must be entirely free from fear, other- 

 wise its attention is diverted from the act to be performed. When 

 the white rats first came under my care they were so timid that 

 they could not be induced to perform the simplest acts. It was 

 only through careful handling, and feeding them from my hand 

 that their fear gradually disappeared. They were also frequently 

 placed in the experiment-box, so that they were thoroughly familiar 

 with it before the experiments were begun. 



In the second place the experiments must be of such a nature 

 that the rat is not required to perform any movements that are not 

 natural to it. Pushing ''with the nose, climbing, digging, and 

 grasping with the teeth and forepaws are movements that a rat 

 naturally makes. No experiment was used that could not be per- 

 formed by one or more of these movements. 



In the third place the inducements for the rat to perform the act 

 must be made as great as possible. The desire for food and com- 

 panionship produced the most vigorous action. It was very diffi- 

 cult, however, to regulate the diet of the rats satisfactorily. If 

 they were under-fed in order to induce them to make vigorous 

 efforts to get the food placed on the outside of the experiment-box, 

 they declined in strength and vigor; if they were given plenty of 

 food they would not make any great effort to perform the required 

 act. The best results were obtained by giving them enough food 

 that they liked fairly well to keep them in good condition, but using 

 as an mducement to the performance of the required act food of 

 which they were particularly fond. Cheese and " Egg-O-See" came 

 in this latter class. 



The experiments were generally conducted in the morning, 

 from nine to ten o'clock. The rats were fed once a day, and the 

 time of feeding was immediately after the experiment. 



II. EXPERIMENTS. 



Experiment I . Climbing a Wire Ladder. 



Method. — A glass jar 40 cm. in height and 15 cm. in diameter 

 was fitted with a cover, in the center of which a large hole had been 



