488 JOHN LINCK ULRICH 



These observations point inevitably to the fact that learning 

 the inclined-plane problem is alone effective when the extensor 

 thrust is used. Other methods used are ineffective in propor- 

 tion to the functional development of the rat. At times, con- 

 secutive perfect records are produced with several imperfect 

 records intervening. More frequently such consecutive records 

 are made before the end of the sixtieth trial, sometimes much 

 before this trial, and thereafter none appear. In a few instances, 

 when in the early trials consecutive perfect records are pro- 

 duced, none are made even after 125 trials are given. A repe- 

 tition of the number of trials does not then improve learning. 

 Often only isolated perfect records are produced. In such cases 

 directive integration is facilitated, but the plunging of the plane 

 the first time progression occurs to it, is impossible. The ineffec- 

 tive responses produced are not conditioned by inadequate 

 excitations in the senses, but by the undeveloped organism. 



From the records obtained, from the behavior of the rat 

 before the plane, little can be said of the significant part played 

 by the senses. Knowing the functional condition of the organ- 

 ism, it would be needless to over estimate its importance in 

 learning as has generally been done. When considering the 

 importance of the reflex mechanism and the changes in behavior 

 brought about by their fluctuation, rather less importance must 

 be attributed to the part played by the senses. Responses, 

 whether adequate or inadequate, are produced by excitations in 

 the external senses, and an exclusive role in learning to be mainly 

 attributed to the senses is an exaggerated estimate of their 

 importance. 



For several reasons the importance of the senses in learning 

 must be reconsidered. The use of other methods than the 

 extensor thrust is not the result of sensory discrimination, nor 

 the product of their excitations, as must be supposed if the 

 freedom of choice of a method is left to the rat. By the very 

 few perfect records produced when the reflex mechanism of the 

 rat is undeveloped, it is seen that the external senses cannot 

 improve upon a method. Fluctuations in the reflex extensor 

 thrusts have alone been observed to improve, temporarily, a 



