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■ 100+ DAYS OF AGE 
E3 100 TO 259 DAYS OF AGE 
□ 260+ DAYS OF AGE 
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IT02 3 TO 104- 
NUMBER OF DAYS INTERVENING BETWEEN CAPTURES, 
c!X- 
Figure 143. — Weight loss between first and second captures during periods when traps were left continuously set. The number 
of observations is listed at the top of each column. Mean weight loss: (1) 2.9 percent when 1 to 2 days intervene between 
captures,- (2) 6.3 percent when 3 to 1 0 days intervene. 
of 5.8 percent in body weight, following an average 
elapsed time of 8 days between captures. 
i. The question of secondary increases in the rate of 
growth. As already mentioned there were no known 
conditions which might be definitely correlated 
with the observed instances of increase in rate of 
growth. The assumption is implicit that, if stress 
from social interactions inhibits growth, when 
growth rate increases the rats concerned must be 
experiencing less stressful situations. Most of the 
increases of growth rate for males did occur during 
the winter when strife was reduced. Adaptive be- 
haviors such as migration or shifts in activity 
periodism may also be involved. 
j. Age and the maintenance of weight. Few rats 
lived long enough to be designated as aged. For 
females there was a slight decrement in weight 
after 450 to 500 days of age (charts 33 and 34, fig. 
141). The two introduced males (Nos. 8 and 12) 
who must have been over 600 days of age at death 
showed declines of 40 to 60 grams in weight during 
the last 100 to 150 days of life. 
k. Place of birth and growth. Rats born in the 
alleys lived nearer to the source of food than did 
those born in the areas. This placed the alley-born 
rats at an advantage with reference to the energy 
they had to expend in going back and forth between 
their home and the Food Pen. A more significant 
difference relating to place of birth was superim- 
posed by the social organization of the population. 
Rats living in the areas were forced to pass near 
the place of residence of others living in the alleys 
when they went to the Food Pen. Thus, the area- 
born rats were exposed more frequently to the 
adverse action of psychological drubbings or terri- 
torial behavior exhibited by the alley-inhabiting 
rats. 
That a differential in growth and maintenance of 
weight did result, which favored the alley-born rats, 
is clearly shown in table 61. For the purposes of a 
2X2 table Chi Square test of significance of this 
data the rats were assembled into those which grew 
larger and maintained their weight better (i.e., 
Maturity Index, 1.0 to 1.79) versus those which 
235 
i 
