OLFACTORY BULBS OF THE ALBINO RAT 221 
ings showed only the activity of the rats when the cage revolved 
and were therefore incomplete, since some rats learned to play 
from side to side of the cage and keep it from revolving, while 
others learned to run up the middle of the sides in such a way 
as to hold the cage at rest. But most of the rats soon learned 
to run the cages and appeared to enjoy it. 
The rats were fed on the same diet as the controls and all the 
animals were weighed at intervals of about two weeks. 
3. Series D. Rats in revolving cages for thirty days 
There were but two litters in this series. One litter was 
weaned and set aside at thirty-five days of age and the other 
at forty days. Both litters were subjected to exercise in the 
revolving cages for a period of only thirty days. All were 
killed at the end of the thirty days of exercise. 
a. Results. The exercised males of these two litters gained 
more rapidly in both weight and body length than did the 
controls, while the females fell behind. The superior growth 
of the test males was sufficient to bring the averages for both 
males and females up to 113 per cent of the weight of the con- 
trols and to 104 per cent of the length (tables 13 and 14). 
The records of the activity of Series D were accidentally 
destroyed, but as these were for a period of but thirty days, 
they would be of little value save in adding further evidence 
that the female rat becomes active sooner than the male. 
While, on the average, there is no difference in the absolute 
brain weight of the test rats in Series D from that of the controls, 
when both are compared with the reference table values in The 
Rat (Donaldson, 15), according to the method there suggested 
(pp. 4 and 5), yet I believe the bulbs do show, even after this 
short period, some effect of the unusal activity (tables 13 and 14). 
In the females, the bulbs make up 4.46 per cent of the brain 
weight in test rats as compared with 4.36 per cent in the controls. 
With the males, the difference was more marked—4.55 per cent 
in tests to 4.20 per cent in controls, making a joint average for 
males and females of 4.51 per cent in tests against 4.32 per cent 
