228 CAROLINE M. HOLT 
TABLE 19. SERIES E 
Test animals 
Albino rats kept in revolving cages for one hundred and three days after weaning 
Males : 
OLFAC- 
OLFAC- TORY AVERAGE 
ANIMALS acu | weionr | canara | waren | uum |rmsomne| amas 
WEIGHT BRAIN PER DAY 
WEIGHT 
days ‘ grams mm. grams grams 
Xe 134 233 193 1.927 | 0.079 | 4.12 4.6 
Vit asec cn aR eo 135 188 195 1.693 | 0.070) 4.16 5.4 
ET RN penta 135 226 198 1.849 | 0.080) 4.30 5.6 
Y7 135 237 205 1.875 | 0.085 | 4.54 8.9 
Average males....... 221 198 1.836 | 0.079 | 4.28 6.1 
Females 
XEN al RPI 10s testo oeeve 134 151 177 1.661 |unequal 4.5 
BY cot ene Pee ere is sccke pee 135 157 181 1.655 | 0.081 | 4.80 aD 
Lge tee oto ME 135 162 180 1.796 | 0.078 | 4.32 4.4 
WG 135 169 191 1.693 | 0.079 | 4.64 6.8 
Averages females.... 162 184 1.715 | 0,079) 4-60 5.8 
Average males and 
females. seas ce- 196 192 1.784 | 0.078 | 4.41 5.95 
As we see, the brains of the initial controls for the test animals 
(X, Y, Z) averaged but 91 per cent of the weight of the initial 
controls for the final controls (L, N, O, T, U, V); the olfactory 
bulbs but 89 per cent. Since it has been found that brain and 
olfactory bulb weight are pretty uniform for any given litter, 
and that when we find light or heavy brains or bulbs in the initial 
controls, we are fairly sure of finding the same relative develop- 
ment in the adult animals of the same litters, it seems fair to 
assume that normal adult individuals of litters X, Y, Z, would 
have had relatively lighter brains and bulbs than were found 
in adults of litters L, N, O, T, U, and V._ If this assumed relation 
were true, then the results given in tables 19 and 20 doubtless 
would fall into line with those of previous experiments in which 
exercised rats showed an increase in brain weight over the 
