480 JOHN LINCK ULRICH 



learning of the problem, require slow development of interaction 

 of body parts for the production of effective movement. Thus 

 the effect of the production of numerous movements upon 

 learning is frequently observed, and these movements are not 

 made before the solving of the latch-box problem, so that the 

 " successful" movement can appear, or in the inclined-plane 

 problem so that eventually one movement may become " suc- 

 cessful." 



This gradual development of interaction of body parts for the 

 production of effective movements in rats when reflex excit- 

 ability is low or hyponormal, is indicated by the observations 

 of the behavior of rats. Usually in the first few trials move- 

 ments are chiefly confined to the problem box. In a few addi- 

 tional trials progression from different positions under the hood 

 covering the problem box is increasingly in the direction of the 

 plane, and at times, it can be seen that vision aids direct pro- 

 gression to it% This behavior occurs more often in some trials 

 than in others, and is always indicative of important changes 

 that are to follow. These repeated advances to the plane are 

 shown in tables 13 and 15 by increases in time required to plunge 

 the plane, but are not to be found in tables 11 and 12 where the 

 reflex extensor thrusts of the rats are stated as functionally 

 fairly well developed and reflex excitability is manifest. These 

 increases appear in the records of rats in which either the reflex 

 extensor thrusts are undeveloped or when reflex excitability is 

 hyponormal. In some instances when excitability is hypo- 

 normal, advances to the plane are so frequent that solution of 

 the problem in one or two successive trials does not take place. 

 This is shown in table 15. Even when the problem remains 

 unsolved, these numerous movements or advances to the plane, 

 produce important changes in learning. In the next trial or 

 two, improvements in all responses follow, and either move- 

 ments are noticeably more directive or, one part of directive 

 integration, progression to the plane or to the door after the 

 plane is plunged, is facilitated. Sometimes with the occurrence 

 of numerous movements and an increase in time, there takes 

 place a decrease in the number of movements, and in the time, 



