30 GARDNER CHENEY BASSET 



In Plate VII is shown the curve of learning (left) and of re- 

 learning (right) of the inbred rats compared with those of the 

 normal ' control. These curves are constructed from figures 

 given in Table IV. The curve of the inbred rats is indicated by 

 the solid line, that of the normal control by the broken line. 

 The ordinates give the average daily time in seconds for each 

 group, and the abscissae the number of the day in which such 

 time was made. The time rec^uired by both inbred and control 

 rats for the first four days was so long that it is represented here 

 by figures and does not appear in the curve. Both learning 

 curves are irregular, but on the eleventh day that of the control 

 passes permanently below that of the inbred. The curves of 

 relearning show that the inbreds had failed to benefit by practice 

 to so great an extent as the normal control. 



V. EXPERIMENT 3: THE INCLINED PLANE 



The apparatus used in this experiment was the same as that 

 used in Experiment 2 : the Preliminary Inclined Plane. The 

 animals were prepared in the same way as for the previous 

 experiment, and began work at the age of seventy days. Sixteen 

 males and fourteen females from the inbred strain were used and, 

 as control, an equal number of males and females from the normal 

 series. Of the inbred rats, fifteen were from the seventh genera- 

 tion, fourteen from the eighth, and one from the ninth. As the 

 behavior of the single ninth generation rat did not vary greatly 

 from the average of the eighth generation, her results have been 

 included in the tables and curves of the eighth generation. The 

 stimulus used in this experiment was the same as in the two 

 preceding, bread soaked in milk. 



Cumulative time was used in recording the earlier trials as in the 

 previous experiment. When the rats began to succeed in entering 

 the food box within the half hour, each one was required to open 

 and enter the food box three times each day. At the end of the 

 third trial it was allowed to feed in the box for five minutes, but 

 was permitted no more food until the completion of the next 

 day's experiment. Each rat was used daily until it had learned 

 the problem perfectly, the criterion of perfection being three 

 perfect trials for each of three successive days. A perfect trial 

 consisted in running from the entrance to the point of operation 

 on the plane at the rear of the food box, opening the door, run- 



