SS NAOKI SUGITA 
as a detailed description of the size of each cell type and its 
mode of enlargement according to age will be the theme of a later 
paper. 
To represent the relative cell density in the cerebral cortex 
for each brain weight group, the sum of the cell numbers in the 
lamina pyramidalis and the lamina ganglionaris, given in table 
3, was used, in order to balance, in some measure, the inequality 
of the cell distribution. These values are given in table 7, 
column C, and in chart 2 (graph N). Both table and chart 
show that the number of nerve cells in a unit volume of the cor- 
tex decreases very rapidly during the first ten days after birth 
(up to the brain weight of 0.95 gram) and after that time it 
decreases slowly but steadily as the age advances. The cell 
number at maturity. is nearly one-fifth the value at birth. 
J. Values for the computed number of nerve cells in the entire 
cerebral cortex, according to brain weight 
The number of nerve cells given in table 3 does not means the 
actual volume of complete cells contained in a unit volume, 
because the parts of cells which showed a nucleus but no nu- 
cleolus in the section were also counted. In spite of this, the 
number in the table indicates fairly the relative number of cells 
or the relative cell density at different ages in the localities 
examined, and from this we may be able to get some indication 
as to the number of nerve cells in the entire cerebral cortex. 
If the actual number of cells in a unit volume be proportional 
to the number of cells counted, the number of cells in the entire 
cerebral cortex may be indicated (theoretically) by this number 
multiplied by the number obtained by dividing the volume of 
the entire cerebral cortex by the unit volume. 
The actual volume of the cortex was not measured, but the 
computed volume is indicated by the following formula, as 
explained already. 
BY RS |S OE (all in millimeters) 
So, if N means the cell number in a unit volume (for example, 
