Berry, Imitation in White Rats. 335 



made. From a wooden bar placed across this hole a string hung 

 down to within 5 cm. of the bottom of the jar. The purpose of 

 the experiment was to discover whether the rats would climb 

 out of the jar by means of the string. Rats Nos. i, 2, 3 and 4 

 were tested, each being put in alone and left in the jar until he 

 ceased to make any particular effort to get out. Every rat tried 

 to get out by climbing up the side, and every rat took hold of the 

 string with his forepaws, but not one made any attempt to climb it. 



I now substituted for the string a wire ladder made of wire net- 

 ting of a centimeter mesh. The ladder was 5 cm. wide and long 

 enough to reach from one side of the bottom of the jar to the top 

 of the opposite side. A small box containing food was placed on 

 top of the jar beside the ladder. Food was also placed at fre- 

 quent intervals on the ladder. 



Results. — No. I when put into the jar ate all the food on the lad- 

 der that he could get by standing on his hind legs. After a few 

 attempts he ceased trying to get the food that was just out of reach. 

 He was in the jar twelve minutes in all. 



No. I was now taken out and No. 2 put in. No. 2 climbed the 

 ladder and entered the box in less than five minutes. 



The next day No. i was again put into the jar by himself. As 

 before, he ate the food within reach but made no effort to climb 

 the ladder. After fifteen minutes No. 2 was put in with him. No. 

 I looked on while No. 2 climbed out, and in less than five minutes 

 followed him to the top of the ladder. He then returned to the 

 bottom of the jar, but in about two minutes he again climbed the 

 ladder, this time entermg the box at the top of the jar. 



No. 4 when put into the jar by himself climbed out in less than 

 a minute; No. 5 got out in fifteen seconds; No. 6 in three minutes; 

 and No. 7 in seven minutes. No. 3 ate the food within reach but 

 made no effort to climb the ladder, although he was left in the jar 

 twenty minutes. No. 4 was now put in with him. He saw No, 

 4 climb out but made no effort to follow him. The next day No. 3 

 was again put in by himself. He ate all the food within reach and 

 stretched to the extent of standing on one leg in his vain efforts to 

 seize the food that was just out of reach. He soon gave up and 

 remained quiet. After sixteen minutes I put No. 4 in with him. 

 But No. 4 would not climb the ladder. Both rats seemed to be 

 cold and refused to make any particular effort to get out. No 

 further trials were made with them. 



