32 GARDNER CHENEY BASSET 



ning around and entering the box, all within four seconds; but, 

 if the time consumed in opening the box after passing the entrance 

 was more than two seconds, or if the time consumed in entering 

 the box after having opened the door was more than two seconds, 

 the trial was considered a failure. Thus it was possible for a rat 

 to have a perfect trial in as long a total time as four seconds, or a 

 failure in a less total time. Those rats failing to learn within one 

 hundred days (three hundred trials) were no longer used for 

 experimentation. Those rats learning the inclined plane were, at 

 the conclusion of the experiment, fed for sixty days in the runway. 

 At the end of this period they were tested for absolute retention 

 and relearning. 



Three of the rats formed the habit of lifting the plane at the 

 end nearest the food box and thus formed the contact, but this 

 method apparently affected neither the rapidity of each trial 

 nor the number of days required for perfect learning. One of the 

 normal rats placed his nose between the electrical contacts and 

 received a shock, but other than one squeal and a vigorous 

 rubbing of the nose, he showed no evidence of harm and had 

 apparently forgotten the experience the following day. Some 

 of the rats jumped to the point of operation from a distance; 

 some placed the fore paws on the end of the plane and pressed 

 down; and still others ran slowly around to the plane, halting 

 an instant on the point of operation, and then continued the run 

 around to the door. As a rule, the last made the best time. As 

 in the maze experiment, many of the inbred rats were subject to 

 errors which persisted throughout the experiment. In particular 

 may be mentioned one rat that invariably formed a loop in the 

 course from the entrance to the point of operation. 



The shortest period of time required by an inbred rat to learn 

 the inclined plane perfectly was twelve days ; by a normal con- 

 trol rat, nine days. Eleven inbred rats and one control failed 

 to learn the inclined plane within the one hundred days allowed. 



In Table V is presented a comparative summary consisting of 

 the daily averages of the entire inbred group and, directly 

 beneath, the corresponding daily averages of the entire normal 

 control group. The inbred rats required, on the average, 73.70 + 

 days to learn the inchned plane; the controls but 45.97 + 

 days. The absolute retention of the inbreds was, on the aver- 

 age, 31.842 seconds; of the controls, but 22.587 seconds. All 



