INTEGRATION OF MOVEMENTS IN LEARNING IN THE RAT 421 



manifest by rats. It will be noticed that only in one rat were the 

 reflex thrusts functionally developed, and in all other rats these 

 thrusts were undeveloped. Reflex excitability is recorded as 

 hypernormal, or hyponormal. When reflex excitability was hy- 

 ponormal the solution of the problem occurred from the second 

 to sixth day or it did not take place. Two rats, in which unde- 

 veloped reflex thrusts existed used the teeth to raise the latch 

 instead of the neck reflex. 



Observations of the movements of the rats presented on this 

 table indicate once more that the essential condition necessary 

 to the production of the neck reflex is posturing, and in the act 

 of posturing the extensor thrusts are important. Likewise, a 

 position of the body is effective in producing adequate extensor 

 thrusts, and this is in accord with the findings of Beritoff (16) 

 with decerebrate cats, that a position is effective in producing 

 increase extensor tone of the limbs with a change of the position 

 of the head in space or dorsally extending the tail. The extensor 

 thrusts are best evoked in reflex excitable specimens, and when 

 these specimens are resting on their feet or on their backs, and not 

 on either side. This statement is also of interest in that reflex 

 excitability does not increase the extensor tone of the limbs unless 

 the body of the animal is in either of these two positions. It is 

 evident, then, that an effective position, such as resting on the 

 feet, would be the best for the interaction of the mechanism of 

 the reflex extensor thrusts, and that for the production of reflex- 

 excitability, and much more so would these reflex mechanisms 

 become effective when an increased number of body reflexes come 

 into use as is the case when posture is attained under the latch. 



Rats not manifesting reflex excitability would necessarily show 

 contrary results from those just mentioned. Not alone is posture 

 not produced, but, as previously stated at the end of the first 

 trial of 30 minutes, or at the end of the sixth trial, when the 

 problem remained unsolved, some rats were greatly exhausted. 

 When the reflex extensor thrusts of these rats were tested at the 

 end of the first of succeeding trials, they were found to be absent 

 or noticeably weak. These observations are in accord with 

 those made by Sherrington (17), in decerebrate animals, that the 



