RETENTION OF HABITS BY THE RAT 7 



has progressed to such an extent that it seems advisable to wait 

 until histological examinations of the brains can be made before 

 describing the lesions in detail. Fourteen animals have been 

 operated upon for destruction of the frontal lobes and of these 

 eight have been autopsied. In these the gross lesion has been 

 in every case as extensive as that indicated in figure 2, and in 

 three of the animals has extended back so as to involve the 

 anterior two-thirds of the cortex. 



Brief records of the animals studied are given below. When- 

 ever possible, fifteen trials in the maze were obtained from each 

 animal on the day following the operation. The time con- 



FIG. 2. DIAGRAM OF THE EXTENT OF THE LESION IN RAT HI 9 , AS DETERMINED 



BY GROSS DISSECTION 



sumed in each of these trials in going from the starting compart- 

 ment to the food dish and the number of errors, either of enter- 

 ing the cul de sac or of turning back upon the true pathway, 

 was recorded. In the following records the total time consumed 

 in these fifteen trials and the total number of errors are compared 

 with the total time and errors of the first fifteen trials made by 

 the same rat in its first training in the maze. The time and 

 number of errors of the rat's first trial in the maze at the begin- 

 ning of training are also compared with those of the first trial 

 of the retention tests. In addition to this observations are 

 reported on the general behavior of the animals in the maze. 



