INTEGRATION OF MOVEMENTS IN LEARNING IN THE RAT 417 



a greater interaction of body parts. Limitations to learning are 

 dependent upon this development of a greater interaction of 

 body parts. 



Before proceeding with the results obtained from the investi- 

 gation of the reflex mechanism of extension and flexion of the 

 rat's limbs and its connection with the learning of the latch-box 

 problem, it is well to consider the mechanism for the production 

 of reflex excitability. The assumption from early observations 

 of rats that reflex excitability was the product of a mechanism of 

 some kind, is in line with the statement of Beritoff (15), that in 

 decerebrate animals, reflex excitability is often manifest, and 

 that in such preparations the extensor tone of the limbs is the 

 best. It seems true from another point of view that the mechan- 

 ism for its production interacts with that of body reflexes, in- 

 clusive of extension and flexion of the limbs, in that in rats in 

 which excitability is manifest, the solving of the problem is cer- 

 tain. One unfortunate thing, is that the degree of the develop- 

 ment of the mechanism for the production of reflex excitability 

 is difficult to judge. This is particularly unfortunate since the 

 degree of the development of the extensor thrusts can be judged, 

 not through observations of the behavior of the rats in the prob- 

 lem as is the case with reflex excitability, but through actual tests 

 on the rats. The only evidence of the degree of the development 

 of reflex excitability is to be recognized in the appearance of rapid, 

 slow, or constant activity, or in the absence of activity. Reali- 

 zation of the mechanism of reflex excitability is accordingly, far 

 from being as tangible as the realization of the mechanism of 

 the extensor thrusts. Degrees of reflex excitability manifest in 

 rats may be conveniently designated as hypernormal or hypo- 

 normal. 



When the reflex thrusts are symmetrically developed and reflex 

 excitability is hypernormal, the latch box is soon solved. Early 

 solving of the problem comes as a result of the fundamental 

 integrated reflex movement being effectively performed, and a 

 number of ineffective movements are not made. Usually pro- 

 gression occurs around the problem 3 or 4 times with 1 or 2 

 posturings and touches of the under surface of the latch and the 



