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ZOOLOGY: BENEDICT, FOX AND BAKER Proc. N. A. S. 
the rhinoceros (living in an environmental temperature of 19.5° C), 
a value but slightly higher than that found with the two elephants. Ac- 
cording to Dr. Blair the rectal temperature of the rhinoceros ranges from 
99.7° F. (37.6° C.) to 100° F. (37.8° C). Our single observation of the 
rectal temperature of this animal showed a value of 37.4° C. 
Although considerable difficulty was experienced in securing the skin 
temperature of the hippopotamus, sufficient measurements were obtained 
to give a fairly clear picture of the probable temperature distribution. 
The temperatures ranged from 20.8° C. on the back to as high as 30.9° C. 
on the belly. An average figure for the temperature of the whole skin 
is probably not far from 25° C. In general the lower part of the body 
was found to be much warmer than the back, the temperature differences 
being greater with the hippopotamus than with the other three animals. 
This may be partly due to the fact that there was considerable vapor- 
ization of water from the skin, for the skin of the hippopotamus was much 
moister than that of the other two animals, although he had been out of 
water for several hours in an environmental temperature of approxi- 
mately 19.5° C. prior to the actual temperature measurements. As a 
matter of fact, the temperatures of the dry and wet bulbs near the animal 
were 19.6° and 11.9° C, respectively. We have been unable to find any 
records of the rectal temperature of the hippopotamus. 
To sum up, then, it can be seen that this group of animals, with a rectal 
temperature essentially that of man, lives in captivity in a temperature 
environment of about 19.5° C. with a continuous surface temperature, 
on the average, but 6 to 7 degrees above the environmental temperature. 
Man, independent of external temperature as a result of the use of clothing, 
has adjusted himself to a very much higher skin temperature, although 
this is still a greatly variable factor, averaging under clothing not far 
from 33° C. The direct measurement of the heat loss of these huge 
animals presents engineering problems rather difficult to solve. It is to 
be hoped that the indirect method of calorimetry (through the measure- 
ment of the oxygen consumption and the carbon-dioxide production) 
under these conditions of internal, environmental, and skin temperatures, 
may be employed to contribute further to our knowledge of the funda- 
mental laws governing heat loss in the warm-blooded animal unprotected 
by a fur coating. It must be recognized, however, that with the elephant, 
rhinoceros, and hippopotamus, as the name of this group of animals 
implies, extraordinarily thick skins have been developed and thus in a 
way these animals carry around, instead of fur, an extra heavy plating of 
epidermis which, without doubt, measurably retards heat loss. 
The details of this study are to be found published in the American 
Journal of Physiology for July, 1921. 
1 Benedict, Miles, and Johnson, these Proceedings, 5, 1919 (218). 
