■J!". -2 ORIGINAL ARTICLES AND CLINICAL CASES 



At the right, below, is a camera outline of a frontal section through the 

 cerebrum at the level of the anterior commissure (except in fig. 12 

 where the section lies at the level of the anterior horns of the lateral 

 ventricles). In these outlines complete replacement of nervous structure 

 by scar tissue or amorphous material is indicated in solid black ; marked 

 degeneration with some nerve elements intact is shown by stippling. 



In the records of training and retention the "number of trials 

 required for learning" represents the number of times that the animal 

 traversed the problem box from the starting compartment to the food, 

 before thirty consecutive trials were made without entrance into the 

 dark alley. Ten trials were given each day in training and retention 

 tests except where indicated. The records of these trials are given as 

 horizontal rows of figures, each number representing the number of 

 trials, in the ten of that day's practice, in which errors were made. 

 Thus in the record of No. 17, 4:2:1:2, &c, means that on the 

 first day four of ten trials contained errors, on the second two of 

 ten, &c. Five errors in ten trials shows no discrimination. When 

 no error is made for thirty trials, it is rare that errors occur in 

 later trials unless the animal is disturbed by being roughly handled or 

 by some new elements in the situation, such as those introduced by 

 scrubbing the problem box. 



The Formation op Habits after Destruction of the Stimulable 



Areas and the Caudate Nuclei. 



The formation of maze, latch-box, and visual habits after destruction 

 of the stimulable area in the rat has been reported in earlier papers 

 [10, 12]. In the present study I have attempted to train animals after 

 destruction of both the stimulable areas and the caudate nuclei. Only 

 three animals have survived the operation long enough to give evidence 

 of learning and they have formed only simple habits. The individual 

 records of these animals follow. 



No. 17. l Adult male. — The cautery was plunged into each caudate 

 nucleus and the frontal pole of each hemisphere was incised. Training for 

 visual discrimination was begun eight days after operation. For several days 

 be spent most of the time climbing to the top of his cage and falling back to 

 the floor. When placed in the problem box he promptly climbed out and 

 repeated this more than two hundred times in spite of severe punishment. He 



1 For convenience in reference these animals are numbered consecutively with others of 

 the visual series wbich have been reported earlier [10, 11]. 



