220 NAOKI SUGITA 
tion in somewhat retarded, because, according to the investiga- 
tion of Watson (’03), myelination in the corona radiata should 
have begun at eleven days and radiations into the cortex should 
have been recognized at twenty-four days. But a more detailed 
test for this process is required before any special use can be 
made of the results. 
14. RELATIVE QUANTITIES OF THE ALCOHOL EXTRACTIVES 
In my former paper (Sugita, ’17 a) a chart, based on the data 
given in ‘The Rat’ (Donaldson, ’15), was presented to show the 
absolute quantity of solids contained in the Albino brain accord- 
ing to the brain weight. For comparison with this, I calculated 
also the relative quantity of alcohol-extractive substances in the 
Albino brains, as shown by comparing the initial weight of the 
brain with its weight after extraction by 80 per cent alcohol 
(for twenty-four hours) and 90 per cent alcohol (for twenty-four 
hours) according to a uniform procedure. As the brains were 
treated uniformly throughout the investigation, the results are 
comparable among themselves. 
The results from 120 normal albino rat brains, grouped in 
twenty brain-weight groups (Groups I to XX), are given here in 
table 15 and plotted also in chart 1, in which the smooth curve 
(in a dotted line) represents the percentage weight of the ex- 
tracted brain on the fresh brain weight. In chart 1, the graph 
which presents the absolute amounts of solids (in grams) accord- 
ing to the brain weight is also given in a solid line based on the 
chart in my former paper (chart 12, Sugita, *17a). It was 
remarked previously (Sugita, ’17 a) that in the Albino brains 
weighing between 0.95 gram and 1.4 grams, that is, between ten 
and thirty-five days of age, the rate of increase in solids is some- 
what higher than in the periods before and after that phase, 
and this fact was formerly interpreted as indicating that, during 
this phase, the myelination in the brain had been proceeding 
very actively. This interpretation is now supported by the 
graph which gives the percentage weight of the brain. This 
graph varies inversely to the amount of the alcohol-extractives 
