Table 62. — Body / weight ratios at 200 days of age 
B/W ratio 
Class 
interval 
Born 1947 or March to 
April 1948 
Born May-October 1948 
Total 
Male 
Female 
Males 
Females 
Males 
Females 
STOUT 
.452 
.471 
1 
3 
1 
1 
0 
5 
2 
6 
2 
15 
0 
23 
3 
9 
8 
8 
2 
27 
4 
13 
7 
7 
6 
33 
5 
3 
6 
5 
16 
30 
6 
0 
5 
1 
5 
11 
7 
1 
0 
1 
3 
5 
8 
0 
1 
2 
2 
5 
9 
1 
0 
1 
0 
2 
.835 
. 928 
10 
0 
0 
1 
1 
2 
36 
30 
42 
35 
THIN 
Mean ratio . 
. 565 
.628 
.574 
. 684 
Table 63. — Mean changes with age for those males which were stoutest at 200 days or age ( i.e ., B/W = .452 to .529) 
No. 
Mean 
lifespan 
maturity 
index 
Time born 
Age in 
days 
Length (B) 
in mm. 
Weight (W) 
in gr. 
B/W 
9 
I. 21 
April 1947 through April 1948 
200 
254 
511 
0. 498 
U17 
262 
539 
. 486 
1 14 
I. 69 
May through September 1948 
200 
252 
491 
0. 511 
1 324 
258 
487 
. 528 
1 The mean age during the April to June period of the year following their birth. 
1 Two of the 16 males listed in the first 2 class intervals of table 62 died before they were a year of age. 
I therefore conclude that the Life Span Matu- 
rity Index better reflects the relationship of stress 
to growth than does the B/W ratio for the arbi- 
trarily selected age of 200 days. 
It was pointed out on pages 95 to 99 that 
the frequency of entering traps increased for rats 
born later in the history of the colony, and the 
assumption was made that frequency of entering 
traps was a direct reflection of the degree of stress 
experienced by a rat. See in particular table 14 
which shows that lateness of birth, frequency of 
entering traps, number of wounds received, and 
inhibition of growth tend to be associated. 
f. The time between litters as this influences com- 
petition and growth. Litter 13 (charts 21 and 24, 
fig. 139) was the only litter born in the pen which 
was conceived on the night of the birth of the 
previous litter by their mother. There was only 
23 days difference in the age of these litters and both 
were known to nurse at the same time in the same 
nest cavity. Whereas any preweaning inhibition 
of growth of the second litter may be a direct 
232 
