408 JOHN LINCK ULRICH 



muscles that would at all times maintain the animal in a position 

 for solving the problem. These last muscles embrace those of 

 the limbs, trunk, neck and head that aid the posturing of the 

 body for the production of the neck reflex to raise the latch. 



If our description of the behavior of the rat is a correct one, 

 the increase reflex-extensor tone in anti-gravity muscles must 

 necessarily be more manifest in those rats that show reflex ex- 

 citability. Beritoff (13), who has also investigated the increase 

 extensor tone in all limbs with the changes of the position of the 

 head and tail in space, states that reflex extensor tone is more 

 readily obtained in reflex excitable specimens than in those speci- 

 mens that do not manifest reflex excitability. Such experiments 

 as have already been performed with rats have shown that a 

 greater interaction of the body parts is present at all times in 

 those forms that were reflexly excitable. Moreover, it appears 

 that reflex excitability is given expression by increase extensor 

 tone of muscles rather than in flexion of the muscles. 



To determine to what extent the position of the labyrinth of 

 the ear, or the head in space, and the extending of the tail dor- 

 sally, increased the extensor tone of the limbs, or resulted in 

 modification of reflex posture in rats, over 300 rats were tested 

 and examined for the extensor tone of the limbs and their inter- 

 action with the reflexes of the trunk. Any manifestation of reflex 

 excitability was noted when making these tests. Our aim here 

 is to confirm such points as were derived from direct observation 

 of the behavior of rats in the problem, and to determine if possi- 

 ble any variation in the mechanism of reflexes, and in the produc- 

 tion of reflex excitability which would effect learning. The test 

 of the rat's reflexes were made before each trial and, occasion- 

 ally, after the interval of thirty minutes when the latch-box 

 remained unsolved. 



Before the method of the examination of reflexes was perfected, 

 it became evident that the reflexes evoked in the living rat could 

 not be regarded as producing alone increase extensor tone of the 

 limbs in decerebrate rigidity, but revealed variations in extensor 

 tone of rhythmic extension and flexion of the limbs or a single 



