50 

 diet are more.*easy to control, though even here, especially 



in the diet, difficulties are found. One rat may gain fat 

 very rapidly on a small quantity of simple food such as 

 bread and milk, whereas other rats will require a variety 

 of food. Therefore, before anything can be concluded 

 from the effects of the number of trials on learning, bet- 

 ter methods must be devised for measuring retention. 

 But something must be said of the retention of organized 

 or integrated movements. These were often as perfect 

 as when learning was completed. A slowness of action 

 was alone evident in the movements, but usually when an 

 initial start was made speed was regained. When, in lift- 

 ing the latch of the latch-bos, a rat would, hold its 

 snout for a short time close under the latch before mak- 

 ing a movement upward to release it from the notch. 

 With the . inclined plane bos, there was occasionally a 

 hesitation in pushing down the plane, and successive at- 

 tempts were made before this was finally accomplished. 



