100 K. S. LASHLEY AND S. I. FRANZ 



in the region of the external capsule opposite the corpus 

 striatum with degeneration of the fibers and cortex laterad to it, 

 and invasion of the cerebral peduncle in the region receiving 

 fibers from the mesial surface of the frontal pole. 



Bilateral destruction of the cortex above the knee of the corpus 

 callosum with degeneration on the orbital and mesial surfaces of 

 the left hemisphere was followed by a partial loss of the habit in- 

 cluding the definite mode of depressing the plane. 



Experiment 23. The frontal areas of the cortex were tran- 

 sected through two trephine holes in a small male rat, 149 days 

 old. He had been trained previously on the inclined-plane 

 box for 100 trials. The average time for the first five trials of 

 practice was: to plane, 332 seconds; to door, 48 seconds. The 

 average time for the last five trials was: to plane, 10.2 seconds; 

 to door, 2.2 seconds. During the training he developed an 

 absolutely stereotyped method of tripping the plane. He ran 

 first to the door, jumped up from there upon the food box in 

 such a way as to alight upon the free end of the plane, turned 

 and jumped down to the floor in front of the door and went in 

 to the food. 



Retention was first tested on the second day after the opera- 

 tion. The animal was fairly active, sniffed at the door of the 

 food ,box and stood up and sniffed the plane repeatedly but 

 made no effort to get upon the box in thirty minutes. On the 

 fifth day after the operation he first showed marked activity 

 comparable to that of a normal animal. For the first four 

 trials he climbed to the top of the box always from the door, 

 but gave no specific reaction to the plane, in each case pushing 

 it down apparently by chance and using a different method 

 each time. On the fifth trial he went first to the door, jumped 

 up upon the lower end of the plane, then turned quickly and 

 jumped down to the door. This was repeated five times before 

 he alighted on the outer end of the plane. During the next 

 ten trials he invariably jumped up from the front of the box to 

 the plane, and then down to the door again, repeating this per- 

 formance as often as fifteen times in a single trial before he 

 alighted on the free end of the plane. This was due in part to 



