INTEGRATION OF MOVEMENTS IN LEARNING IN THE RAT 497 



box remain unlearned, whereas in only two rats, judging from 

 the number of consecutive perfect responses made, was the 

 inclined-plane actually learned. This is because the effective- 

 ness of posturing and the production of the neck reflex to raise 

 the latch is greater than the effectiveness of posturing and the 

 production of the extensor thrust or any other method that 

 plunges the plane. When the latch is raised by the neck reflex, 

 the head of the rat is moved upward which increases the extensor 

 tone of both fore limbs, and decreases the extensor tone of the re- 

 flexes of the hind limbs. The opposite effect is produced when the 

 head is lowered, the fore limbs are flexed and the extensor tone 

 of the hind limbs is increased. Now it is the last condition that 

 exists when posture is usually attained before the plane, the 

 head tends to be lowered when posturing, and no increase in the 

 extensor tone in the fore limbs is given, so that the extensor 

 thrust to plunge the plane can be produced. The head is, 

 however, raised when the reflex thrusts of rats are well devel- 

 oped, and this is accomplished by crouching the body. In 

 the two rats in which the extensor thrusts were exclusively used, 

 the body was crouched with the head raised some time before 

 the plane was reached, and when the plane was approached, 

 the head was raised still more and the extensor thrusts of both 

 or of one limb plunged the plane. Thus, two rather similar 

 postures are demanded, one to produce the neck reflex and the 

 other the extensor thrust; but to produce the extensor thrust 

 requires a better developed reflex mechanism. When the 

 reflexes are undeveloped, progression is rapid to the plane and 

 other methods are used to plunge the plane. The development 

 of interaction of body parts to attain posture to perform funda- 

 mental movements is then impossible. 



In the investigation of learning the inclined-plane problem, 

 there is no physiological necessity for the acceptance of any 

 antithetical division of movements and the retention of the 

 "successful" or the "congruous" movements, for in the inclined- 

 plane problem, it is difficult to say when such movements are 

 produced. Pleasure cannot be said to produce fixation of move- 

 ments in learning; for the supporters of "pleasure-pain" would 



