INTEGRATION OF MOVEMENTS IN LEARNING IN THE RAT 461 



effective thrust was discovered, one or both fore limbs were used 

 to plunge the plane, and no part of the body, with the exception 

 of the head of the rat, was at any time directly over the plane. 

 The weight of the body was not an additional aid in bringing 

 the plane down. In all previous work in animal behavior, the 

 adjustment of the mechanism of the problem to produce the 

 most effective response, and an interest in the nature of a defi- 

 nite effective response have been neglected. In the past the 

 thing of the greatest interest seemed to be the production of a 

 " successful movement" and its " retention." 



When an adequate plane was constructed, an effective ex- 

 tensor thrust was, in only a few instances employed for succes- 

 sive trials. It is scarcely necessary to recall the fact that in 

 most rats these extensor thrusts are functionally undeveloped 

 or that an unequal antagonistic action of the extension and 

 flexion of the limbs exists, and only in rare instances are the 

 thrusts developed or an equal antagonistic action of the limbs 

 prevails. Fluctuations in the extensor thrusts occur in every 

 case when an unequal antagonistic action is present. Of the 

 250 rats actually experimented with in the inclined-plane prob- 

 lem, only two rats were obtained in which the thrusts were fairly 

 well developed. All other rats when tested, evoked a left or 

 right ipsilateral fore reflex thrust, or the extensor tone of one 

 fore ipsilateral thrust was stronger than the other when the head 

 of the rat was passively bent to one side of the midline of the 

 body, or when the head was dorsally extended 45 degrees of this 

 line. The hind reflex thrusts were strongly evoked backward in 

 a fixed position or rhythmic extension and flexion of them 

 occurred. In some rats, the fore reflex extensor thrusts could 

 not be evoked, and in others all reflex thrusts were absent. 



For the present, it is convenient to consider only the method 

 used on the first trial to plunge the plane, though a later method 

 must at this time be incidentally mentioned to give significance 

 to the one used on the first trial. The use of more than one 

 method makes an investigation of learning rather difficult. 

 Frequently many rats were used to clear up or substantiate one 

 particular . observation. 



