66 K. S. LASHLEY 



5. Does the motor area (determined by electrical stimulation 

 and effects of destruction upon motor coordination) act as the 

 final common path for learned reactions, or may the efferent 

 impulses of learned reactions be transmitted from other regions 

 (section VI)? 



The methods employed were essentially those devised by 

 Franz for the study of the frontal lobes; training the animals 

 before or after operative destruction of cerebral areas and com- 

 paring their learning ability with that of normal animals. 



Operative technique 



The operations were performed under deep ether anesthesia. 

 In every case a median longitudinal incision was made through 

 the skin from the base of the skull to the anterior margin of the 

 orbits, the hair having been removed by a depilatory. The skin 

 was then drawn back to expose the entire dorsal surface of the 

 skull. The operative field was mapped out in relation to the 

 skull sutures and an opening of the required size was made with 

 trephine and bone forceps. In case of bilateral operations the 

 skull openings were made on both sides of the longitudinal 

 suture to avoid injury to the longitudinal sinus. 



The cerebral cortex was destroyed either by cauterization or 

 by cutting it away from the underlying tissues with a cataract 

 knife. For cauterization a small electric cautery was used, but 

 owing to the quick cooling of its point and its inconvenient form 

 it proved less satisfactory than the knife. In those experiments 

 where it was used the fact is indicated. As soon as hemorrhage 

 from the brain injury was checked the skin incision was closed 

 by three stitches and covered with a cotton-celloidin dressing. 



Since retention was tested shortly after the operation in some 

 cases the question of irritation from the wound is of importance. 

 In general the animals gave little evidence of discomfort after 

 the operation. In three cases, after almost complete removal 

 of one hemisphere, the animals ate heartily within thirty minutes 

 after recovery from anesthesia. The positive results of the 

 retention tests furnish the best evidence that irritation from 

 the wound does not seriously interfere with the tests, 



