INTEGRATION OF MOVEMENTS IN LEARNING IN THE RAT 419 



than when excitability is hypernormal. Often, as previously 

 stated, when reflex excitability is hyponormal, the problem re- 

 mains after 6 days unsolved. In some cases in rats in which at 

 the beginning of a trial excitability is hypernormal, it later sub- 

 sides and becomes hyponormal. It is once more evident that 

 the solution of the problem is dependent upon a manifestation of 

 reflex excitability in rats, but the efficient manner in which the 

 solution of the problem occurs, is dependent upon the func- 

 tional condition of the reflex thrusts of the rat's limbs. The 

 inefficient ways previously observed to have occurred when 

 solving the problem, may now be accounted for by the unde- 

 veloped condition of the reflex extensor thrusts. One way, the 

 use of the teeth to raise the latch out of the notch, is of particular 

 interest. A different method to solve the problem comes about 

 as a result of the functional undeveloped condition of the extensor 

 thrusts and not because of repeated trials or successive " efforts." 

 The use of the teeth is the direct result of the ineffective produc- 

 tion of posture to produce the neck reflex; yet posture of a kind 

 to raise the latch with the teeth is observable. Both the produc- 

 tion of this posture and the use of the teeth are modifications of 

 posture and the production of the neck reflex movement, for when 

 the mouth is opened the fore limbs are extended and the hind 

 flexed in the manner employed with the production of the neck 

 reflex. In both instances the fore quarters are raised and the 

 hind flexed. This reflex phenomenon is more evident when 

 the jaw is lowered with the opening of the mouth than when the 

 head is dorsally extended. It has been noticed that when the 

 teeth have been used for a time, and a decided fluctuation in 

 the reflex thrusts occurs, the neck reflex may be used instead of 

 the teeth to raise the latch or vice versa. 



These factors that determine the solution of the latch-box prob- 

 lem are presented in table 3. The effectiveness or ineffective- 

 ness with which the latch was raised out of the notch to open the 

 door of the problem is not indicated in this table, but this will 

 be given in other tables in connection with learning. In the 

 present table are indicated the develoment of the reflex thrusts, 

 their stability or instability, and the degree of reflex excitability 



