GROWTH OF THE CEREBRAL CORTEX Ty | 
for the same age, which belong to brain weights higher by about 
10 per cent. 
Let us take as an example an underfed brain which weighs less 
than 1.0 gram for examination. ‘The computed volume of the 
cerebral cortex is in the underfed smaller on the average by 16 
per cent than the standard for the same age (chapter 9). As 
shown by calculation, the computed number of nerve cells in the 
entire cortex is almost the same in both the standard and the 
underfed, throughout all ages, so that the process of cell division 
appears to have been going on undisturbed by the condition of 
underfeeding. The cell density, the cell size, and the cortical 
volume must therefore be regulated so as to provide the cerebral 
cortex with the number of cells fixed according to the age, regard- 
less of the starvation. 
To present the relation, the formula N x L.F x W.D x T 
was used. The value.of N <x L.F x W.D x T has proved in 
my present material from the underfed to have been 1.7 per cent 
higher than the standard, but as this is open to some correction, 
it may be regarded as approximately the same in both the under- 
fed and the corresponding standard. ‘To be less in the cortical 
volume, which was computed by the formula L.F x W.D x T, 
by about 16 per cent or more, the cell density must be increased 
by about 19 per cent or less theoretically. ° This latter figure is 
fairly in accord with that obtained in my direct observation; 
that is, 17 per cent excess in the number of cells in a unit volume 
in the underfed brains (chapter 10). To be reduced in cortical 
volume by 16 per cent or more, the individual cell must theoret- 
ically be reduced in volume also in the same ratio, in order not to 
be reduced in total number. My results in cell-size measurement 
showed that the individual cells measured are reduced in average 
diameter by about 12 per cent, and accordingly in average volume 
by about 30 per cent or more. These figures appear somewhat 
higher than was to be expected, but it must be recalled that these 
figures apply only to the largest cells found in the measured 
locality, and this class of cells may suffer a disproportionate 
arrest, so that the figures do not indicate what has taken place in 
the small cells and those of average size. Furthermore, in the 
