GROWTH OF CEREBRAL CORTEX 5 
corresponding to a brain weighing 1.161 grams (body weight 
19.7 grams, body length 86 mm., tail length 47 mm. and age 
estimated at about 10 days), while the relative volume of a 
cerebrum in the last entry, Group N XXIII (table 2), is 
16.55 < 16,30 x 10.25 = 2765.09 (see also table 3 A) 
corresponding to a brain weighing 2.345 grams (body weight 394 
TABLE 3 
Giving the relative cerebral volumes, obtained by the formula: W.B X L.G X Ht., 
for each brain weight group of the Norway (A) and of the Albino (B). The albino 
rat brain weight corresponding to the given Norway brain of the same age, obtained 
by reducing the Norway brain weight by 18 per cent, is also given in (A) 
(A) NORWAY RAT | (B) ALBINO RAT 
235, EES 
. = 5 ol Si ‘3 5 
28 ee Observed 3 g2 zo 
Brain weight paleulsted 2kSos | Brain weight brain weight eee ae 
weigh Soe 4 ache : Soeal a 
w SIP paola ®welshe| the Albino | 33238 |  # UP | Albino rat | ES ES 
N XXIII r'"| brain of the] + 3X3 Sak PS 
D same age Bo m2 IX—xx ee 
Norway rat = ore 
sone based on table 3 
oa8 (Sugita, 717) 
jan] 
grams grams grams 
N XI 1.161 0.952 1547 9) LX 0.954 1335 
N XIII 1.356 ee, S259 illite 1.047 1356 
N XIV 1.436 A ALPE 1844 | XI 1.156 1522 
N XV 1.536 1.259 1944 } XII 12253 1606 
N XVI 1.644 1.348 2040 || XIII 1.334 1663 
N XVII 1.743 1.429 2189 — | XIV 1.449 1788 
N XVIII 1.836 1.505 DOTA. | kV 1.558 1956 
N XIX 1.965 TOU, 2407 Ie NeVGE 1.662 2014 
N XX 2.033 1.667 2442 FDA Ie W330 PMY 
N XxI 2.164 1.774 2634 i XeValiah 1.832 2228 
N XXII 2.266 1.858 PHT A ee; 2) D8 1.924 2285 
N XXIII 2.345 1.923 2765 KX 2.037 | 2568 
grams, body length 256 mim. and tail length 202 mm.). <Ac- 
cording to these determinations, the volume increases by 79 per 
cent while the weight increases by 102 per cent, showing roughly 
that the specific gravity of a brain in the fully mature Norway 
rat is higher than that of younger one. 
By an estimate based on the data given by Donaldson and 
Hatai (11), it would appear that, if the Albino and the Norway 
