refer to one or more captures of an individual rat 
during separated periods of capturing. The total 
times handled (row T) is not as accurate an index 
for judging the probability of observing the condi- 
tions, since these conditions rarely changed in a 
given rat during a single period of trapping, and 
since males reentered traps (repeated) more fre- 
quently than did females. It is quite apparent 
from table 65 that males are much more predis- 
posed to conditions terminating in ill health or 
mortality. Also refer to figure 147. 
Table 65. — The sexual differential in susceptibility to ill 
health and in probability of mortality 
Comparison from table 64 
Chi 
square 
Probability of 
chi square 
Row E to Rows R + S 
7. 72 
Less than 0.01. 
Row L to Rows R + S 
5. 54 
Less than 0.02. 
Row P to Row Q 
14. 77 
Less than 0.01. 
e. Relationship of growth ( Maturity Index) to health 
and mortality. The question arises: “Do those con- 
ditions which alter growth also alter the likelihood 
of the individual’s experiencing those conditions of 
ill health and mortality which were observed in the 
experimental population?” In order to answer this 
question related groups of data presented in table 
64 were lumped together. All duplications were 
eliminated, so that each rat is represented only once 
in each major category. Littermates not charac- 
terized by each condition were compared with 
those so characterized. A summary of this is given 
in table 66. 
Combat Injuries: The difference of 0.30 in the 
Maturity Indices for males is believed to be biologi- 
cally significant. It represents an average dif- 
ference of 26 grams at 196 days of age. The 
important point here is that the rapidly maturing 
males are more likely to engage in competition 
with similar males for priority of action. Less 
rapidly maturing males are in early life conditioned 
to avoid competitive situations, and are thus less 
likely to receive extensive wounds. See table 67 
for additional information. 
Having a “ cold From table 66 it is quite apparent 
that rats which are subject to having colds are not 
only members of litters with an inhibited matura- 
tional pattern, but they themselves have the poorest 
maturational pattern. It is presumably the inhib- 
ited pattern of maturation which predisposes the 
rats to contract colds, rather than the possession of 
colds which produces an inhibited pattern of 
maturation. This is shown by the fact that most 
of the rats having colds were recorded as having a 
Maturity Index in the Class III range just prior to 
contracting the cold. 
Rats having ectoparasites: The data in table 66 
indicates that there is no correlation between pat- 
tern of growth and likelihood of having those 
ectoparasites which were present in this population- 
Table 66. — Maturity index in relation to health and mortality 
Health and mortality categories 
Males 
Females 
Number 
Mean 
maturity 
index 
Number 
Mean 
maturity 
index 
Combat injuries (mostly), Rows A to D of table 64 
42 
1.82 
17 
1.97 
Negative littermates 
34 
11.12 
24 
1.82 
Rats which had a cold, Row F of table 64 
13 
11.53 
4 
11.29 
Negative littermates 
14 
11.19 
10 
1.93 
Rats having ectoparasites, Rows H to J of table 64 
29 
1.85 
10 
1.92 
Negative littermates 
44 
1.98 
12 
1.92 
Rats born in 1948: 
Lived over 150 days but died before May 1949 
16 
1.95 
6 
1.95 
Lived to May 1949 
49 
11.05 
46 
1.93 
Rats which died between 50 and 1 50 days of age 
29 
11.25 
6 
11.31 
242 
