INTRODUCTION 



In reviewing the field of animal psychology the fact 

 becomes evident that no special phase of retention has 

 ever been studied to any great extent, nor has there been 

 to date any single research devoted entirely to this subject. 

 The need of some definite knowledge, other than what is 

 speculative, concerning the nature or characteristics of 

 retention has been more and more emphasized year after 

 year as the facts of experiment point more inevitably to the 

 conclusion that the basis and foundation of all learning 

 is inseparably bound up with the capability of the organism 

 to retain what has been learned., If what is learned can 

 not be retained, there would be no advance on any line. 

 And if what is learned can be retained, we are vitally con- 

 cerned in possessing all attainable facts which will shed a 

 clearer light on the obscurity of present knowledge on the 

 subject. The present dearth of facts on retention is thus 

 not to be underestimated. 



Experimental literature on the present subject is so 

 limited that the available references covering the history 

 of experiment in retention comprise for the most part only 

 incidental observations, supplementary to experiment which 

 had another specific object. For the sake of comparison 

 the following data has been summarized from these refer- 

 ences in work on animals* 



Kinnaman (1) in his work on the monkey has shown by 

 some brief experiments that, after an absence of 50 days 

 from the problem, perfection in point of speed, and in- 

 cidentally errors, is not as marked as in the last trials of 

 learning. The problem was one of manipulation. Allen's 

 experiment (4) shows that the Guinea Pig retains a simple 

 labyrinth without great loss for 63 days. Porter in his 

 work (5) on the Vesper Sparrow, the Cowbird, the English 

 Sparrow, and the Pigeon shows that retention was good 

 for the first three subjects at 30 days, but there was great 



