RESPONSIVE LIFE OF ORGANISMS 481 



profitable acts, and to lift the latch at once; he has learned 

 by trial and error. 



So we learn in infancy to walk, to talk, to play; and in 

 later life, to acquire any wholly new accomplishment with- 

 out instruction or example. 



Such learning is conditioned upon the possession of a 

 nervous mechanism that is capable of retaining the impres- 

 sions accompanying a former act until the stimulus is 

 repeated. Such a mechanism is, as we have seen, the upper 

 brain in the vertebrates. It is an agency for reviving along- 

 side every important stimulus the impressions that have 

 accompanied former responses to the same kind of stimu- 

 lus, action then being determined in accordance with 

 whether these have been pleasurable or painful, whether 

 they have been successful or unsuccessful in attaining a 

 desired end. The details of the process will be made much 

 clearer by the study of a concrete example. 



Study 63. Learning by trial and error in chicks. 



Materials needed : Healthy young chickens, a week to ten 

 days old; food and water for the chickens. A labyrinth 

 made on the plan shown in figure 269* (one for each group 

 of eight or ten observers) . 



This study consists in observations on the details of the 

 method of a chick in learning the route through the box 

 from one end of it to^the other. Place the chicks as 

 indicated in figure 269; several of them with plate of food 

 in one end of the box, and one chick (the subject of the ex- 

 periment) alone and without food in the other end. The 

 group will feed and chirp contentedly, and the other one, 

 moved by the sound of their social converse and by his 



*This may readily be constructed out of an ordinary wooden 

 cracker box, by adding partial partitions to make the passageway, 

 i, 2, 3, 4. 



