GROWTH OF THE CEREBRAL CORTEX 221 . 
and, as it decreases relatively rapidly in the phase during which 
the brain grows in weight from 0.9 gram to 1.35 grams, or in the 
ages between nine and thirty-three days, it shows that during 
that phase the alcohol-extractives increased. 
The turning points in the both graphs marked with crosses 
x and XxX) and asterisks (* and **), respectively, are in fair 
% ff : mgms. 
68 + 1 | a : ss aay ee = 
| | | | | | = 
66 4 - + | 4 + alba — ~_ les fe 
Sy Tt 
| 
64|—_| 2) Bee ae ne ad ee —— 100 
Sees te | 4 | : 
60|_ i | | | | t 
| Hes PRA Sele OD ih Leet 
O20 03) 1047 (05) 06 FOr 0S 0910 Sse by LT AS oe gms 
Chart 1 The dotted line shows the ratio between the initial brain weight and 
the weight after its dehydration and extraction in 80 per cent alcohol (for twenty- 
four hours) and 90 per cent alcohol (for twenty-four hours) according to a uniform 
procedure, plotted on the brain weight. The data were taken from table 15. 
The graph was drawn connecting the middle points of each pair of entries. 
* and ** indicate the turning points in the graph. 
The solid line shows the absolute weight of the solids in the brain according to 
the brain weight. The data were taken from table 74 in ‘The Rat’ (Donaldson, 
15) and calculated by me. * and ** indicate the turning points in the graph. 
For the ratios of brain weight the scale is given on the left side of the chart and 
for the absolute weight of the solids the scale is given on the right side. 
coincidence, so that it may be concluded that the mass of the 
aleohol-extractives would be in proportion to the grade of myeli- 
nation in the brain, and by following the former the progress in 
myelination could be estimated roughly. 
It must be emphatically stated that my figures given in table 
15 do not represent the total quantity of the alcohol-extractives, 
