224 CAROLINE M. HOLT 
TABLE 15 
Record for Litter W, Series E, showing gain in weight for individuals in revolving 
cages and for centrols 
TEST RATS CONTROL RATS 
We (m) Ws (f) Wi (f) We (m) Wz (m) Ws (f) 
Initial weight........| 44.0g.} 40.5¢.|] 50.5¢.| 438.5¢.| 50.0¢g.| 40.5¢. 
2 weeks weight...... 60.4 62.0 65.6 63.2 68.7 69.2 
4 weeks weight...... 97.0 82.0 103.0 107.0 120.0 89.0 
6 weeks weight....... 139.0 124.0 142.2 139.0 148.8 119.0 
9 weeks weight...... 186.0 142.0 170.5 194.0 212.0 148.0 
30 weeks weight...... 210.0 148.0 187.0 205.0 224.0 150.0 
inal genet neers et: 209 mm.| 182 mm.} 198 mm.} 207 mm.| 200 mm.} 190 mm. 
The test rats from Litter W were, on the whole, slightly longer 
and lighter in weight than the control animals. The majority 
of individuals in Litter W proved to have abnormal brains— 
one or both olfactory bulbs being very much undersized. The 
brains, therefore, could not be used for comparison and the 
litter was excluded from the tables. For comparison with the 
rest of the litters of Series E, it was necessary to use other stock 
litters, as will be described later (tables 18 to 25). The compari- 
sons are not, therefore, of as much value as they would be were 
the controls from the same litter. On the average we find body 
length slightly more, and body weight slightly less, in test ani- 
mals (table 25). I think we may conclude that these results 
agree in general with those of previous investigators indicating 
that exercise has but a slight effect, if any, upon either body 
weight or body length. 
The size of the viscera was considerably modified. These 
results have been incorporated in the report by Hatai (15). 
Activity of exercised animals. These rats showed great 
individual difference in the amount of activity and in the age 
at which they became most active (tables 16, 19, 21, 25). In 
these respects, there was also a considerable difference in litters 
as shown by the following record. 
If we take the record of these same rats for ninety-three days 
we get an average of 5.76 miles per day for males, and 5.96 miles 
