12 JOHN LINCK ULRICH 



of the fact that greater effort was demanded of the rats in the 

 three and five trial groups. 



These curves of integration being constructed on the average 

 time made by all rats, do not express individual differences in 

 learning. Some rats naturally in this respect showed interesting 

 differences in their capacity to learn the problem; the ends of 

 the curves point to where the least adaptable rats left off learn- 

 ing. To indicate where the first rat of each group completed 

 its task a small circle has been added to the curves. These 

 two points, the ends of the curves and the position of the circles, 

 give the extreme individual differences in the power of learning 

 of the rats in this experiment. 



PLATE II 



DISTRIBUTION CURVE 

 LATCH BOX 



BY TRIALS 



The demonstrated fact that one trial daily was more econom- 

 ical than when several were demanded suggested further work 

 with the latch box. It was thought interesting to determine 

 whether fewer trials would be necessary to learn the problem 

 if efforts were distributed over more days. A trial, therefore, 

 was given one group of rats ever>^ other day, and another group 

 every third day, that is, with two days intervening between 

 trials. 



This particular addition to the problem of the latch box was 

 conducted under the .same conditions and with the same strain 

 of rats, the descendants of those previously worked with. A 

 more satisfactory group of rats could hardly have been secured 

 than those used in this experiment, since they were of an un- 

 usually hardy strain. On the intervening days, when the rats 



