GROWTH OF THE CEREBRAL CORTEX 219 
TABLE 14 
Showing for each brain in litter H the sex, the age, the brain weight, and the percent- 
age value of water in the brain, accompanied with the standard values of percentage 
of water in brain for the same age and for the same brain weight. The differences 
between the observed percentages and the corresponding standard values are given 
in special columns, with their averages. ° 
| PERCENTAGE OF i PERCENTAGE OF 
a hee _ WATER ____ WATER 
a a oan Seer on WATER STANDARD FOR THE STANDARD FOR THE 
gaap | saracane | eee [eo vars oo 
grams 
Ha f 13 0.880 86.39 | 85.40 +0.99 | 86.82 —0.43 
b f 17 1.024 84.15 83.82 +0.33 | 85.08 —0.93 
Cc f 23 1.135 2.00 81.93 +0.07 83.21 —— el 
d f 28 1.166 80.83 80.74 +0.09 | 82.70 — 1°87 
e m 32 1.215 80.31 80.04 +0227 81.70 —1.39 
f ay ff Thal 80.12 79.55 +-Okot | 838.78 —3.66 
g m 43 1.295 80.24 | 79.32 +0.92 80.56 =(0.32 
AVeTage ls) 2) hn: +0.48 —1.40 
that the underfed brain is slightly underdeveloped for its age, 
but somewhat overdeveloped for its weight. Similar relations 
have been revealed by the comparisons already made. Normally 
about 0.5 per cent excess in percentage of water in the brain would 
mean at the early ages approximately one or two days’ retarda- 
tion in development (compare table 74 in ‘The Rat,’ Donaldson, 
Zo) 
From the same litter (Litter H) I took with each of the above 
individuals a second rat for the study of the myelination, because 
it is known that the percentage of water in the brain is correlated 
with its myelination. The brains under seventeen days of. age 
showed no fibers in the frontal sections, as stained with Pal- 
Kultschitzky method. The twenty-eight-day brain showed 
only a few faintly stained fibers in the cortex, the fibers in the 
corona radiata (designated C. E. by Watson, ’03) being already 
myelinated. Material above thirty-seven days was not exam- 
ined. This passing examination of a small number of cases 
roughly indicates, therefore, that the first appearance of myelina- 
