24 K. S. LASHLEY 



25.9 rb 1.5, thus considerably greater than that in group B, 

 since the object of the experiment was to test the effects of 

 the longer interval on recovery from extensive injury. The 

 total extent of the lesions is shown in text figure 3. Con- 

 stants for the group are given below: 



Trials Errors 



Initial learning, 146.0 ±: 8.8 41.7 ± 2.9 



Preliminary retention tests, 4.8 ±0.7 



Postoperative retention tests, 93.0 ±: 9.5 20.4 ± 2.1 



Average per cent destruction, 25.9 ± 1.5 



The average loss in this group is very much greater than 

 that in group B (63 per cent loss as against 33 per cent). 

 Judged on this basis, the longer rest period following opera- 

 tion did not reduce the amount of practice necessary for re- 

 learning, but a better estimate of the effects of the rest period 

 may be gained by comparing groups with equal amounts of 

 destruction. For this purpose similar constants have been 

 computed for the fifteen cases of group B having the greatest 

 cerebral lesions (nos. 84 to 98, inclusive) and are given below. 



Trials Errors 



Initial learning, 138.7 ± 11.4 50.5 ± 3.1 



Preliminary retention tests, 0.8 ± 0.2 



Postoperative retention tests, 74.0 ± 4.7 25.2 ± 5.7 



Average per cent destruction, 23.8 ± 1.2 



The average extent of lesion in these cases from group B 

 is very close to that of group C. In retention tests group C, 

 with the longer rest period after operation, is inferior as 

 judged by trials and superior as judged by errors, but the 

 differences are in neither case significantly greater than their 

 probable errors. 



The loss from disuse shown by the preliminary retention 

 tests is somewhat greater after the fourteen-day interval than 

 after the seven-day, but is not sufficient to mask a recovery 

 from operative shock, if this had occurred. The experiment 

 proves that no better retention records are made after the 

 fourteen- than after the seven-day rest period following oper- 

 ation. Since, as was pointed out above, all the animals of 



