BRAINS OF EUROPEAN AND AMERICAN RATS COMPARED 91 
water, organic matter and salts in them and by their thickness. 
Watson (’06) has shown that the constitution of the osseous sys- 
tem of the rat can be significantly modified by diet. 
In the meantime it is clear that we cannot infer that the brain 
weights in the several Norway series are related precisely as are 
the cranial capacities. 
CRANIAL CAPACITY CHART 5 oy 
24 Ge: ] . 
23 23 
NORWAY Bs 
— ——— PHILADELPHIA RECORDS ° 
24 e EUROPEAN RECORDS 2.1 
2.0 2.0 
Bs 19 
18 18 
nf 17 
6 ~ ALBINO. ig 
—— PHILADELPHIA RECORDS 
5p x EUROPEAN RECORDS — 415 
14h 1.4 
BODY WEIGHT gms. 
3 
80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 S 
Chart 5, cranial capacity based on European series only. Showing the cranial 
capacity in cubic centimeters of the Europeanseries of Norways all combined, 
contrasted with the computed value (formula 1) for the Philadelphia records and 
similarly of the European series of Albinos all combined, contrasted with the com- 
puted value (formula 2) for the Philadelphia records. @ = European series— 
Norway. X = European series—Albinos. 
However, bearing in mind that the cranial capacities of the 
three European Norway series combined are probably as much as 
2.1 per cent too low, and that so far as the tables 13 and 18 and 
chart 4 show, the capacities of the combined European albino 
series are slightly (1.6 per cent) above those for the Philadelphia 
Albinos, it is possible to make a general comparison between the 
two forms as found in Europe, in respect to their cranial capacity. 
The data for this comparison are found in tables 12 and 13 
and the averages for the European series there given are plotted 
