Table 64. — Summary of health and mortality 
Row 
Item 
Number of 
males 
Number of 
females 
Total 
A 
Extensive body injuries 
21 
5 
26 
B 
Blind (26) and face cut (4) 
21 
9 
30 
C 
Tail injuries 
6 
7 
13 
D 
Feet injuries 
9 
0 
9 
E 
Total body injuries — Total A to D 
57 
21 
78 
F 
Had a cold 
16 
5 
21 
G 
Ill health — general 
13 
7 
20 
H 
Ticks and fleas 
6 
0 
6 
I 
Lice (common to abundant) 
19 
7 
26 
J 
Warbles-infections 
13 
10 
23 
K 
Tilt-headed 
2 
2 
4 
L 
Total F to K 
69 
31 
100 
M 
Mortality- (found dead) 
20 
8 
28 
N 
Anesthesia or exposure in traps 
9 
3 
12 
O 
Disappeared 
44 
12 
56 
P 
Total mortality total M to O 
73 
23 
96 
Q 
Surviving to May 1 949 
50 
53 
103 
R 
Total rats weaned 1947 and 1948 
123 
76 
199 
S 
Total recaptures (7 + days) 
490 
400 
890 
T 
Times handled 
970 
723 
1693 
E + L+P 
199 
75 
284 
dog tick, Dermacentor . The state of lice infestation 
was not always recorded, but, on many records it 
was noted that no nits or lice were present. Pre- 
sumably, self-grooming and possibly also mutual- 
grooming was responsible for the low prevalence 
of lice. 
Row K, Tilt-headed Rats: Presumably the four 
rats who walked about with their heads perma- 
nently twisted to one side had arrived at this 
state as a result of a middle ear infection, Strepto- 
bacillus. Despite this condition, one of these rats 
was the most dominant individual about his 
burrow. 
Row N, Dead from Anesthesia or Exposure in Traps: 
Included here are those rats dying from exposure 
to cold or heat while in traps or those given too 
much anesthesia. The preponderance of males 
possibly indicates their lowered resistance. 
Row O, Disappearance: Fifty-six rats disappeared 
sometime between the time of their last capture 
and the period during May and June 1949, when 
all rats still living were captured by excavating all 
burrows. Probably no more than 10 or 12 rats 
became the prey of owls, cats, and opossums which 
managed to circumvent the various barriers sur- 
rounding the quarter-acre pen. All the remainder 
are presumed to have died from various causes 
and to have disintegrated without ever being 
found. Several were found so decomposed, and 
their remains so scattered, that their metal ear tags 
could not be found. It is believed that no rats 
escaped from the pen. The preponderance of 
males in this category again indicates their greater 
susceptibility to mortality factors. 
These 13 categories of ill health or mortality 
were recorded primarily at times when the rats 
were captured and handled. Therefore, the prob- 
ability of observing some condition characterizing 
a rat should be approximately proportional to the 
frequency with which it was captured. Rows R 
and S in table 64 show that there were 613 hand- 
lings of males and 476 of females. These instances 
241 
