62 A Reconstruction of the Nuclear Masses in 



NUMBER OF CELLS IN INFERIOR OLIVE. 



In order to obtain an approximate idea of the number of cells in the 

 inferior olivary nucleus, calculations based on different methods were made. 

 All of the methods used had to do with the volume of the nuclear material 

 comprising the olive. This was determined, as already mentioned, by the 

 displacement of water by the model. This volume was determined as 460 

 cubic centimeters for the magnification of 15 diameters. From this, the 

 actual volume of the olive was found to be 0.14 cubic centimeter (460 cubic 

 centimeters divided by the cube of 15). To determine the number of cells 

 per cubic centimeter of nuclear material in the olive, counts were made of 

 the cells occurring in the olivary masses, as follows : 



(1) The total number of cells occurring in the olive in one section were 

 determined by actual counting of all nuclei by means of traveling back and 

 forth with a mechanical stage. Then the area of the olivary convolutions 

 was obtained by means of a perimeter and the volume computed bj' multi- 

 plying the perimeter value by the thickness of the section (40/x). The volume 

 containing these cells was controlled by cutting out in wax the magnified 

 drawing of the olive in that section and determining the volume of the wax. 

 By this method the olive was found to contain 950,000 cells. 



(2) The area of a high-power field of the microscope was determined 

 by measurement and the volume of the field comi;)uted by multiplying the 

 area by the thickness of the section. All the cells were then counted in a 

 number of fields and the average value used in the computation for the total 

 number of cells. By this method, which may be considered as fairly accurate 

 as soon as one learns to count accurately the cells in a field, the nuclei 

 in the olive were found to be 1,050,000. This value is an average of many 

 counts, the highest being 1,068,000 and the lowest 1,038,000 by this method. 



(3) The third method used for determining the cells in the olive was 

 that of counting the cells occurring in a definite square projected into the 

 field of the microscope from squared centimeter paper by an Abbe camera 

 lucida. The exact size of this field could be determined readily by measuring 

 a ruled slide (0.1 millimeter) in terms of the centimeters on the squared paper. 

 The volume of this sciuare was then determined by multiplying the area by 

 the thickness of the section. Further computations were then made to 

 secure the number of cells in the total volume of the olive. By this method 

 the total number of nuclei in the olive was found to be slightly less than 

 1,100,000, and a value but slightly above that determined by counting the 

 total cells in the measured microscopic field. The nucleoli were also counted 

 by this method and found to be 530,000 in one inferior olivary nucleus. 



Considering the second and third methods to be far more accurate than 

 the more laborious first method, it may be said that the total number of 

 nuclei (both of ganglion and neuroglia cells) in one inferior olive is between 

 1,000,000 and 1,]0(),()00; the number of nucleoli is about 500,000. These 

 counts were made in conjunction with Dr. fossick, to whom credit for the 

 methods used is gladly given. 



