A. The Repeat Response. Traps were left set for 
3 to 8 days during each period of trapping. Any 
rat caught before the terminal day of a period of 
trapping had the opportunity of being trapped 
during a later date of that same trapping period. 
Such captures following the lapse of 1 to 7 days were 
designated as repeats. 
Only 30 percent of the rats (195 out of 652), 
captured initially during trapping periods, re- 
peated. For those rats which did not reenter 
traps during a trapping period, it may be assumed 
that confinement in traps comprised such an 
unpleasant experience as to override the attraction 
to enter the trap exerted by the bait. Even among 
those rats which repeated, (table 9) some delayed 
reentrance longer than did others. This suggests 
that, even among the minority who were quite 
prone to reenter traps, some were affected more 
by the experience than others. Furthermore, the 
decline in frequency of longer intervals before 
repeating suggests a possible regularity to the 
intensity of the effect of being trapped. Any such 
regularity was obscured by three variables in the 
manner of assembling the data: (a) Trapping 
periods were not all of the same duration, and 
thus the longer repeat intervals did not have the 
same opportunity of occurrence as the shorter 
ones, (b) Rats repeating once were released, and 
thus were subject to being captured a third time, 
(c) The number of rats available for trapping 
was not constant (see fig. 10). 
Table 9. — Frequency of repeat intervals 1 
Interval length 
in days 
Males 
Females 
Total 
Expected 
frequency 
1 
129 (126.0) 
51 (56.0) 
180 (182.0) 
. 7001 
2 
35 (39.5) 
22 (17.5) 
57 (57.0) 
. 2193 
3 
10 (10.7) 
2 (4.7) 
12 (15.4) 
. 0593 
4 
5 (3.04) 
1 (1.35) 
6 (4.39) 
. 0169 
5 
0 (0.74) 
1 (0.33) 
1 (1.07) 
. 0041 
6 
1 (0.05) 
3 (0.024) 
4 (0.078) 
. 0003 
Total 
180 
80 
260 
1. 0000 
1 The numbers in parenthesis refer to the number of each interval calculated on the 
basis of the expected frequency. 
In calculations not included here, these three 
variables were taken into consideration. It was 
found that for those rats which did repeat, the 
probability of the number of rats waiting 2 days 
before repeating was 0.50 of the number waiting 
only 1 day; the number waiting 3 days was 0.50 
of those waiting 2 days; and so on. Empirically, 
a probability of 0.50 gave a better fit than did 
either 0.49 or 0.51. The observed and expected 
frequencies of repeat intervals (table 9) approxi- 
mate each other so closely that confidence may be 
placed in the notion that there is a regularity to 
the change in frequency of intensity of response to 
traps among the members of the population. 
1 his regularity is probably that determining the 
right hand one third of the curves shown in figure 
77. 
B. The Recapture Response. When traps were left 
unset for 11 to 75 days (mean, 46 days) and then 
reset it was again possible for rats to reenter. A 
capture after such a lapse of time is termed a 
recapture. 
A certain proportion (c.f. fig. 10 and first five 
points in fig. 78) of both males and females were 
represented by recaptures roughly parallel to 
their opportunity of being captured. However, 
certain individuals skipped some opportunities of 
capture — that is they avoided reentering traps. 
This resulted in a mean elapsed time between 
captures considerably longer than the mean in- 
terval between exposure to set traps (table 10). 
The actual mean interval between recaptures 
closely approximated 85.12 days rather than the 
46.42 possible or the 67.37 calculated from the 
observed captures. This was because many in- 
dividuals did not enter traps during the terminal 
or last few periods of trapping to which they were 
exposed. 
90 
