346 ^Journal of Comparative Neurology and Psychology. 



bar he did not go out at once, but began to gnaw the string; twice 

 he gnawed it in two, and would have done so repeatedly if he had 

 not been prevented. 



NO. 4 LEARNS TO GET OUT. 

 Date Gets out Time 



The total time it took No. 4 to learn how to get out was one 

 hour, and his method of learning was similar to that of No. 3. 

 At first he tried different places at random until he found the bar. 

 After opening the door two or three times he went directly to it 

 after pulling the bar. If he found the door closed he returned 

 to the bar and pulled it again. 



Experiment VI . Pulling a Knot With the Forepaws. 



Method. — A wooden box 45 cm. long, 39 cm. wide and 13 cm. 

 deep, inside measurements, was covered with wire netting of a 

 centimeter mesh. The door (6x5 cm.) was in the middle of one 

 end of the box. It opened outward and was held shut by a wooden 

 bar on the outside. A string of black thread fastened to the end 

 of the bar extended up and over the box, terminating in a knot 

 about a centimeter above the top of the box, 13 cm. from the near- 

 est side of the box, and 38 cm. from the door. 



In order to open the door it was necessary for a rat to stand 

 on his hind legs, reach up through the top, grasp the knot with his 

 forepaws and pull it down. The knot was too far above the top 

 of the box for him to seize it with his teeth without first using his 

 forepaws. 



It was my purpose to make the act so difficult that no rat would 

 learn to do it by himself. 



No. 2 was first taught to open the door. The knot was lowered 

 until he could seize it with his teeth. Then it was gradually 



