90 K. S. LASHLEY 



out reducing the learning ability of the animals. The greater 

 lesion appeared in number 19 (plate II, figure 19) and this animal 

 required the fewer trials for learning. 



Summary of data 



The tests of the learning ability of animals after destruction of 

 areas of the cerebrum cover practically every portion of the cere- 

 bral cortex. If we include group 2,. every portion is covered but 

 since it might be urged that in hemidecerebrate cases the re- 

 maining hemisphere functions normally it seems best to treat of 

 this group separately. The total destruction in all cases except 

 group 2 and number 17 (animal which failed) is shown in figure 9. 

 In these cases, where the destruction was bilateral and nearly 



FIG. 9. THE TOTAL EXTENT OF DESTRUCTION OP ALL ANIMALS TRAINED ON THE 

 DOUBLE-PLATFORM Box, EXCLUSIVE OF UNILATERAL OPERATIONS 



symmetrical, all of the frontal, dorsal, and occipital region has been 

 destroyed and there remains only a small basilar region which 

 has not yet been explored. I have made many attempts to pro- 

 duce injuries restricted to this area, both by dissection and by in- 

 jection of chemicals, but the operations have always been at- 

 tended by hemorrhage around the medulla which resulted fatally. 

 However, the region is thoroughly covered by one of the hemi- 

 decerebrate cases and this, with the results which have attended 

 operations on other portions of the cerebrum make it practically 

 certain that this unexplored area is of no greater importance for 

 learning than is any other part of the cerebrum. 



The numbers of trials required for learning and the extents of 

 injury to the cerebrum in each animal studied in these experi- 



