94 K. S. LASHLEY AND S. I. FRANZ 



shows that any loss of the habit shown in other animals is prob- 

 ably not the result of operative shock but must be ascribed to 

 the actual brain injury acting either locally in the operative 

 field or extending by hemorrhage or intracranial pressure to 

 other regions. The extensive destruction of the temporal sur- 

 faces of the cortex in experiments 18 and 19 shows that these 

 areas play no important part in the retention of the habit. Fig- 

 ure 7 shows the combined extent of the lesions in these animals. 



Frontal region destroyed: animals showing retention after operation 



Experiment 20. Two trephine holes were made through the 

 calvarium of a large female rat, 140 days old, and a transverse 

 incision was made through the frontal pole of each hemisphere. 

 The animal had been trained for 35 trials on the inclined plane 

 box. The average time required for the first five trials was: 

 to plane, 123 seconds; to door, 42 seconds. The average time 

 required for the last five trials was: to plane, 13 seconds; to 

 door, 3 seconds. 



Retention was tested twenty-four hours after the operation 

 but the animal was stuporous and did not react to the problem 

 box. On the following day she opened the food-box three times. 

 Her movements were slow and much time was spent in scratch- 

 ing at the dressing on her scalp. There were, however, few 

 random movements and except for the diversions incident to 

 this scratching, she kept closely to the direct path from the door 

 to the plane and from the plane to the food. Her method of 

 tripping the catch before the operation had been to walk to the 

 back of the plane and, standing either on or beside it with her 

 hind feet, to reach out to its outer end with her fore feet and push 

 down, gradually throwing her weight forward on her fore feet. 

 This same method was used throughout the trials following the 

 operation, but the movements involved were carried out with 

 greater inaccuracy than before. In some trials she went from the 

 plane to the door without making any attempt to push the 

 former; in others she pushed, but did not wait for the catch to 

 spring. 



