476 JOHN LINCK ULRICH 



required before interaction leading to its facilitation is devel- 

 oped. This gradual development is seen best from the results 

 presented in tables 11 to 15. The first of these tables gives the 

 record of a rat that possessed fairly well developed reflex ex- 

 tensor thrusts of all limbs and manifested hypernormal reflex 

 excitability. The reaction time for the first trial, it will be 

 noted, is very short and that of the second trial still shorter. 

 Moroever the second trial is perfect. There is, because of the 

 good functional condition of the rat, no necessity for a prolonged 

 development of an interaction of body parts to facilitate re- 

 sponses. The behavior of the rat on the first trial showed a 

 high degree of efficiency, for, when this rat was admitted to the 

 problem, progression was rather slow and slightly diverted to 

 the plane, the plane was touched by the fore paws, slight posture 

 was attained, the extensor thrust was produced, then progression 

 was rapid to the front of the problem and slow through the 

 opened door. It may be argued that, on the first trial, progres- 

 sion could have been in any other direction than slightly diverted 

 to the plane, and to the opened door after the plane was plunged, 

 yet this does not preclude the fact that the functional mech- 

 anisms of the rat are fairly well developed. 



Several more trials are required before directive integration is 

 facilitated. Up to the seventh trial, progression is either to the 

 right or to the left of the problem to the plane, and repeated 

 advances to the plane occur. In this trial directive integration 

 is facilitated. Occasionally, throughout learning, the direction 

 of progression to the plane changes, but disruptions in directive 

 integration and an increased difficulty to produce the extensor 

 thrust is not observed to be present. The reason for the slow 

 development of directive integration and the change in direction 

 of progression to the plane, appears to be due to slight fluctua- 

 tions in the extensor thrusts of the fore limbs when the rat's 

 head was passively bent to the right or to the left of the mid- 

 line of the body. The results of other rats presently to be con- 

 sidered, established the statement that fluctuations in an ipsi- 

 lateral fore reflex thrust changes the direction of progression to 

 the plane. When directive integration is facilitated, many 



