GROWTH OF THE CEREBRAL CORTEX 87 
As to the cells in the lamina ganglionaris, the relation is 
somewhat different from that just described. ‘The total number 
of cells, including both the small and large pyramids, decreases 
relatively rapidly after birth, until the brain weight reaches 
1.25 grams (25 days). It then shows a slight increase (table 3, 
Groups XIII and XIV), but decreases again by slow steps and 
remains almost fixed after 35 days (brain weight 1.4 grams) 
at 60. Finally, in old rats, only 50 cells were counted in a unit 
volume of 0.001 mm.,* or about one-fifth the number at birth. 
If the number of the large pyramids alone is considered, then 
the number decreases rapidly from birth to a brain weight of 
0.8 gram (9 days). After this, it decreases slightly and remains 
almost fixed at 23 up to a brain weighing 1.2 grams. In brains 
weighing 1.3 to 1.5 grams it shows a tendency to increase slightly 
for a time—corresponding to the increase in total number of 
cells in this layer (above mentioned)—but finally becomes fixed 
again at 23 to 24 throughout maturity. In old age, it has 
diminished to 20 or about two-sevenths the number at birth. 
The large ganglion cells attain nearly their full size (Cell body 
21u X 28u; Nucleus 184 x 19%) at 0.9 gram in brain weight 
(10 days), almost at the same time as the small pyramids. 
I can not, from the data at hand, satisfactorily explain the 
increase in cell number in the lamina ganglionaris in the period 
during which the brain grows from 1.2 grams to 1.4 grams in 
weight. This fact might however have some connection with 
the chemical structure of the cells and consequently be related 
to a change in reaction to the reagents used, so that the size of 
the large pyramids, after having attained a maximum (21ly X 28.) 
at a brain weight of 0.9 gram, diminishes slightly, at the same 
time that their response to the stain changes somewhat, meas- 
uring only 20u X 27y at a brain weight of 1.3 to 1.4 grams, 
after which they again enlarge to a full size of the cell body 
(sometimes over 23u X 30u). In the ecarbol-thionine staining 
the sections from brains weighing less than 1.0 gram show a 
violet tone, those from brains weighing more than 1.2 grams a 
blue tone while those from brains weighing 1.0 to 1.2 grams are 
intermediate in tone. We shall pass over this question now, 
