GROWTH OF THE CEREBRAL CORTEX 89 
N is 240 for Group VIII, as shown in table 7, column C), the 
relative value of the number of nerve cells in the entire cortex 
may be. computed by the following formula.‘ 
INCL OE SOW). Det (L.F, W.D and T, in millimeters) 
The results of this computation are shown in table 7 and in 
chart:2 (graph NLWT), where the necessary data were all taken 
from the present or former papers and the relative value of 
NXL.F XW.D XT is calculated. For N, the corrected 
sum of the cell numbers in the lamina pyramidalis and in the 
lamina ganglionaris, given in table 3, was used (table 7, column 
C). The results are quite interesting. As seen from table 7, 
columns D and E, and chart 2 (graph NLWT based on column 
’ BE), the relative value of the computed number of cells in the 
entire cortex increases rapidly from birth to a brain weighing 
0.9 gram (about 10 days), and then for a while the increase 
becomes slow up to a brain weight of 1.17 grams (20 days), 
attaining at this time nearly the complete number of nerve 
cells (see graph NLWT, mark X in chart 2). After having passed 
this phase, the value for the number of cells remains almost 
constant throughout the life. The average of the values for 
Groups XI—XX in table 7 is 530, so that between birth and ma- 
turity the number of cells counted has increased two times, 
but nearly al/ of this increase has taken place during the first 
ten days of life. These results coincide very well with the con- 
clusions of Allen (12), that in the cerebrum mitosis continues 
with diminishing activity to the 20th day after birth. 
4 By this computation the number of cells in the entire cortex will be equal 
to the number of times the unit of volume, 0.001 mm.* in which the cells were 
counted, is contained in the entire volume of the cortex, multiplied by the num- 
ber of cells in a unit volume. The number of cells designated by N is however 
the sum of the numbers in two unit volumes, that is, the number in one unit 
volume of the lamina pyramidalis plus the number in one unit volume of the 
lamina ganglionaris. 
Since the numbers of cells used, N, is that in two unit volumes, the fore- 
going product must be divided by two. As dividing the volume of the cortex 
by 0.001 is equivalent to multiplying it by 1000, and as the product must be 
divided by two, the operation may be expressed as follows: 
NXL.F XW.D XT X 500 = Number of cells 
