110 NAOKI SUGITA 
of the values obtained by the above formulas is not allowable, 
since, comparing the areas in the Albino among themselves, the 
fixed coefficients? 1.21 and 0.98 were eliminated from the for- 
mula, as already stated, and similarly in the Norway the corre- 
sponding coefficients’? 1.19 and 0.98 were also eliminated from 
the formula. In order to compare the areas in these two forms, 
the coefficients must be taken into consideration. As the product 
1.19 x 0.98 is higher by 3.6 per cent than the product 1.21 x 0.93, 
the value of L. F x W.D x T for the Norway should be raised by 
3.6 per cent to be directly comparable with the value of L. F x 
: 
W..D Xf for the Albino: ~The’ ratio Pages oe (= 1.036) 
121093 te 
being represented by C, the comparable value of the cortical 
volume for the Norway may be obtained by the corrected formula 
as follows: 
EA X Vie Dax Se € (C1803) 
Table 15 gives the computed cortical volume of the Norway 
brain, obtained according to the above corrected formula, and 
this is shown graphically in chart 4 (graph LWT’). 
As the available data in the Norway do not extend to the 
earlier ages, I could not determine the early increase in the 
cortical volume of the Norway, but our data show that the cortical 
volume is increasing somewhat more rapidly during the period 
when the brain weight is increasing from 1.16 to 1.54 grams and 
after that it increases more slowly but steadily as the entire 
cerebral volume increases, as shown in table 15 and in chart 4 
(graph LWH’). In the Albino, as has been shown, the cortical 
volume increases relatively rapidly until the brain attains 1.17 
grams in weight, a phase which probably corresponds to the 
phase in the Norway of 1.48 grams in brain weight. 
To compare the cortical volume in the Norway rat with that 
of the Albino, I have paired, in table 15, the Norway data 
(L.F x W.D x T x C) directly with the corresponding Albino 
° For a proper comparison, the coefficients here used are those for the same 
brain weight groups compared in both forms, being respectively the averages 
for Groups XIII to XX and for Groups N XIII to N XX, taken from tables 4, 
5, 11 and 13. 
