240 ROBERT S. ELLIS 



or 



CM 



N = ^ X ^M X w 



(!)■ 



As an example we may substitute the values for Case 15035, 

 Area 3, left hemisphere (table 1). 



^^479X30 /82^y, 

 2220 \89.1/ 



= 6.47 X 0.86 X 25 

 = 138 



RESULTS OBTAINED FROM COUNTS 



Neurohistologists who have made a study of the Pur kin je 

 cells are familiar with the fact that these cells are not evenly 

 distributed, but tend to be more or less irregularly spaced, and 

 this seems to be particularly true for the human cerebellum. In 

 the bottom of sulci they are not normally so numerous as they 

 are at the summits of the folia. It would not be far wrong, in 

 fact, to say that they increase in frequency as one passes from 

 the bottom of the sulcus to the summit of the folium. This is 

 probably to be interpreted as incident to the phenomena of 

 growth. The bottom of a sulcus represents an arrest in growth; 

 the summit of the folium is the last to fill out and develop. It 

 is, then, not surprising that a greater number of Purkinje cells 

 should appear in the region characterized by the greatest amount 

 of growth change. 



Considerable variation will be found in the frequency of 

 Purkinje cells, even in adjacent folia. This is especially true of 

 defective brains, less so of normal ones. This makes it necessary 

 to count several hundred cells in order to get a satisfactory 

 average for any given area. Each value given in the tables in 

 this paper is based on an average of about 400 cells, and it is 

 beUeved that by taking a number so large the effects of acci- 

 dental selection have very largely been eliminated. 



If perfectly satisfactory normal cerebella had been used as 

 the basis for the norms given in table 1, it seems certain that 



