6 S. I. FRANZ AND K. S. LASHLEY 



the modal time is about thirty seconds, most of which is spent 

 in exploratory sniffing. With practice these exploratory move- 

 ments disappear and the animal runs to the food without a 

 pause. Many animals come to follow the path marked by the 

 dotted line in figure 1. That is, they keep close to the right- 

 hand wall of the middle alley and keep close to the end of the 

 partition in rounding the turn. This cutting down of excess 

 distance and absence of exploratory sniffing are characteristic 

 of the later stages of learning and when they appear in retention 

 tests are therefore conclusive evidence for at least a partial 

 retention of the motor habits 'of the maze. 



In training, ten successive errorless trials were taken as evi- 

 dence for learning (rarely more than six errors are made in the 

 hundred trials following the achievement of this record) . Some 

 of the rats were then given an overtraining of from one to two 

 hundred trials before the destruction of the frontal lobes. Others 

 were operated upon on the day following that on which learning 

 was completed. 



The operations were performed under ether anesthesia, and 

 at the end the cut scalp was closed with sutures and was covered 

 with a cotton and collodion dressing. 



In some cases a transverse opening about 4 by 8 mm. was 

 made in the skull just back of the front o-parietal suture and 

 the frontal area of the brain was destroyed by passing a narrow 

 scalpel diagonally forward to the region of the olfactory bulbs 

 and thence cutting out to the sides of the cranial cavity. In 

 other cases two small trephine holes were made in the region 

 of the suture and a spear-pointed needle was inserted through 

 these, pushed through the frontal area and drawn to the sides 

 to cut away the frontal regions. Owing to the small operative 

 field it is not possible to determine the exact extent of the lesion 

 at the time of operation but the possibility of using a large num- 

 ber of animals and of later determination of the extent of the 

 destruction of tissue makes it possible to obtain records of some 

 animals in which the exact lesion desired has been produced. 



Most of the animals have been kept for two weeks or more 

 after the operation and in many cases the absorption of the clot 



