172 BRAINS OF RATS AND MEN 



In various operations one entire hemisphere was 

 removed and different parts of the cortex were re- 

 moved from both hemispheres symmetrically. In dif- 

 ferent operations all parts of the cortex (except the ol- 

 factory fields, archipallium) were removed, and the 

 effect on learning a kinesthetic habit (double-plat- 

 form box. Fig. 47, p. 189) was observed (1920, p. 98). 

 The conclusion is that "amounts of injury from 14 to 

 50 per cent of the entire cerebral cortex do not result 

 in any correlation of the learning ability" (p. 100). 

 "There is no evidence that the injuries to the cere- 

 brum resulted in any reduction of the power to learn. 

 .... Whether greater injury than 50 per cent would 

 cause deterioration has not been determined" (p. 



lOl). 



These conclusions apply, of course, only to the 

 double-platform box experiment. They indicate that 

 for this habit no specific localizable cortical field is 

 necessary. This habit, Hke simple maze-running, does 

 not seem to be at basis a cortical function at all 

 (though normally the cortex may participate in some 

 way not as yet determined). Lashley seems to be in- 

 clined to interpret the evidence as tending to show 

 that the entire cortex is equipotential in learning. In 

 reality these experiments shed no light upon the 

 mechanism of cortical participation in this particular 

 learning process, but rather suggest that if this pro- 

 cess reaches the cortical level at all it is only in some 

 way not brought out by the procedure adopted. 



