386 JOHN LINCK ULRICH 



said to be " stamped in," fixated, or be of some consequence to 

 the animal. The present investigation must determine whether 

 the sorting of movements into antithetical sorts is justifiable, and 

 whether, by so doing, the real difficulty in formulating a physio- 

 logical explanation for learning arises. It is necessary to deter- 

 mine, if possible, a factor other than " sensory association" for 

 the so-called retention of movements. It is evident that the 

 most important consideration we are to face is the establish- 

 ment of the relative position of every movement an animal 

 makes before the solving of and during the learning of a prob- 

 lem. Unless observation can throw light upon the relation of 

 all movements, the prevalent antithetical division of all move- 

 ments must remain the very foundation of our theories of learn- 

 ing, and likewise the establishment of " sensory association" or 

 even " pleasure" must still be considered a factor in the supposed 

 fixation of movements. 



II. THE LATCH-BOX PROBLEM 



For the investigation of learning, several problems were se- 

 lected, not so much in accordance with a preconceived plan, but 

 as investigations proceeded some things unrevealed in one prob- 

 lem necessitated the continuation of the work with other prob- 

 lems. The first problem selected, the latch-box, showed limita- 

 tions in respect to the number of solutions, though in a great 

 number of rats learning took place. On the other hand, in the 

 inclined-plane, and in the maze problems, solutions could be 

 easily accomplished, but the number of rats in which learning 

 could be facilitated was not great. The possibility of the exter- 

 nal senses functioning to a greater extent in some problems than 

 in others, led to the use of problems of " discrimination" and of 

 delayed reaction. 



A foremost consideration in the selection of problems was to 

 establish the importance of every movement made while learning. 

 To this end an understanding of the way any problem is solved is 

 dependent upon a knowledge of the range of individual charac- 

 teristic movements made by an animal. Again, an understand- 



