442 HARVEY CARR 



but practically nothing adequate is known of the retentive 

 function as yet. (6) The discrimination experiments were poorly 

 controlled. It is within this field that subsequent work has 

 made its greatest progress. He used two methods, neither of 

 which has been followed. In one a reaction to a given object 

 is inculcated and then similar objects are interpolated in the 

 series of tests. The second, so far as the distance senses are 

 concerned, is much superior to those in use at present. A visual 

 object "a" was placed against a denned background "b, " and 

 the animal was forced to discriminate "a" from "b." Recent 

 unpublished work from this laboratory has demonstrated that 

 when two spatially distinct objects are placed against an un- 

 known background, as is commonly the case, one of the objects 

 may be ignored. (7) The study of the instincts of chicks is 

 excellent and most of the conclusions are yet valid. (8) The 

 significance for intelligence of a development in motor capacity 

 was strongly emphasized, a neglected topic in contemporaneous 

 thought. (9) Animal learning was regarded as a process of 

 association on the sensory-motor level. Animals may and prob- 

 ably do have ideas, but such ideas were not effectively present 

 in their experimental behavior. So far as the reviewer is con- 

 cerned, this conclusion is still valid, as no experiments yet 

 published are convincing as to the presence of ideas. 



Such a summary in comparison with the present status of 

 the science reveals the fact that these studies represent no in- 

 considerable achievement. Some new problems have since been 

 attacked, e.g., the relative values of the different senses in learn- 

 ing, etc. ; the old problems and technique have been developed, 

 but subsequent work has consisted to a large extent in a sim- 

 ilar extended exploration of the animal scale. The author's 

 success seems to be due primarily to his acute and thorough 

 analysis of the human processes involved and to his keen appre- 

 ciation of the logic of experimental procedure. While he robbed 

 animals of their assumed ideational powers, yet he bridged the 

 gap by his insistence upon the prevalence of the trial and error 

 method of learning in the human mind. 



Contemporaneous criticism was severe. The strictures as to 

 the use of "utter hunger," an unfortunate expression, were 

 unjustified so far as fact was concerned. Apology is made for 

 the irritating dogmatic tone often displayed, and for the ten- 



