370 
PACIFIC SCIENCE, Vol. IX, July, 1955 
TABLE 2 
Temperature (C.) of Rattus spp. by Sex 
Rattus he. 
iwaiiensis 
Rattus 
rattus* 
Rattus n 
orvegicus 
Number 
Number 
Number 
examined 
Mean 
examined 
Mean 
examined 
Mean 
Male 
97 
37.5 
81 
37.5 
29 
37.4 
Female 
135 
37.7 
79 
37.6 
19 
i 
37.9 
i 
* Rattus rattus rattus and R. r. alexandrinus 
rat. On the other hand, a rat closely allied to 
the R. rattus group, R. mindanensis , also has 
been found to have a mean body temperature 
of 35.9°C. on Guam (Baker, 1946, ibid.). The 
reasons for these discrepancies are not known, 
but different environmental temperatures on 
Guam and Hawaii may be responsible in part. 
It is of interest to note that the mean body 
temperature of both species of rats on Guam 
was 36.4°C. for females and 35.5°C. for males. 
No such wide differences were noted on Hawaii 
although the females tended to have slightly 
higher mean body temperatures than the males 
(Table 2). 
Data from individual rats recaptured more 
than once indicated a marked variation in body 
temperature. Rectal temperatures in °C. of rats 
recaptured on the dates shown are given in the 
following examples: 
Rattus haw aiiensis; Adult 9 ; 7-1-52, 37.5°; 7-9, 
37.8°; 8-14, 38.0°; 8-21, 38.1°; 10-15, 38.0°; 
10-23, 37.0°. Adult d\ 12-16-52, 37.8°; 1-13- 
53, 39.0°; 2-17, 38.8°; 2-18, 36.1°. 
Rattus rattus; Adult cf ; 12-10-52, 37.8°; 12-11, 
38.1°; 2-10-53, 38.2°; Juvenile 9; 2-15-52, 
39.0°; 2-18, 39-4°; 2-21, 37.8°; 3-4, 38.6°; 3-7, 
37.2°; 3-19, 38.9°. 
Rattus norvegicus; Adult d; 12-5-52, 36.8°; 12- 
16, 37.6°; 12-17, 37.6°; 12-18, 36.6°. 
These data are not unexpected since studies 
on the laboratory rat have shown that the animal 
does not regulate its body temperature efficiently 
(Donaldson, 1924, Amer. Anat. Mem. [Wistar 
Inst.] No. 6 [2nd ed.]). The variable rectal tem- 
perature of small, warm blooded animals may 
suggest that the animal is in part poikilother- 
mous. Nevertheless, this most probably is not 
a valid inference since these small animals show 
a profound physiological regulation but their 
adjustment to environmental changes is subject 
to varying degrees of thermal inertia (Herring- 
ton, 1940, Amer. Jour. Physiol. 129: 123-139). 
On the other hand, all warm-blooded species 
have a diurnal cycle and measurements at differ- 
ent periods in their cycle may affect the tem- 
perature. This may account in part for the 
variability in body temperatures observed here. 
The writer acknowledges the suggestions of 
Dr. Simon Rodbard, Assistant Director, De- 
partment of Cardiovascular Research, Michael 
Reese Hospital, Chicago, who reviewed the 
manuscript. — Leo Kartman, Communicable Di- 
sease Center , Public Health Service , U. S. Department 
Of Health , Education , and Welfare , San Francisco. 
