226 CAROLINE M. HOLT 
TABLE 17 
TEST PAIRS CONTROL PAIR 
W, 21st day after mating, 12 young Ws 24 days after mating, 3 young 
and 61st day after mating, 11 young |and 50 days after mating, 12 young 
W. 102d day after mating, 16 young W. 102 days after mating, 0 young 
pregnant not pregnant 
Y, 22d day after mating, 9 young 
and 67th day after mating, 9 young 
Y; 102d day after mating, 0 young 
not pregnant 
Zs 22d day after mating, 12 young 
and 88th day after mating, 9 young 
Z; 102d day after mating, 0 young 
not pregnant 
It is significant also that the pair making the record of an average 
of 13 per litter for three successive litters, and the control pair 
are from the same original litter. Of course the numbers here 
are too few to enable one to draw conclusions but it would not 
be surprising to find some correlation between the greater weight 
of the sex organs in the exercised rats (Hatai 715) and the fertil- 
ity of these animals. 
Effect on brain and olfactory bulbs. It has already been 
noted that most of the control rats of this series were lost through 
disease. For comparison with the exercised rats, a set of con- 
trols used in Series A of the defective feeding experiment was 
chosen (table 20). These rats seemed better suited for the 
purpose than any others because they had been born at the 
same season as the test animals and reared in the same laboratory, 
so the food from day to day was the same for the two sets of 
rats. Among these, it was possible to find records of eight 
rats of almost the same body length and weight and of approxi- 
mately the same age as the exercised rats killed at the end of the 
experiment. For the four which were mated and not killed 
until they were two hundred and thirty-eight days old, it was 
not possible to get controls of the same age, the four oldest of 
the controls (table 22) averaging only one hundred and sixty- 
nine days and the body length being 6 per cent less than that 
of the test animals. But as these are beyond the one hundred 
and fifty day limit, up to which time the bulbs increase in rel- 
