STUART, D. G. 
o 
its body temperature was around 41 C, maintained visibly active 
circulation in the thin web of the foot when it was kept on a cold 
plate so that the tissue temperature recorded by a thermocouple 
was close to freezing. We have a number of examples of that sort: 
the tail of the muskrat which John Krog and I observed and which 
Kjell Johansen plans to observe further, cools in ice water to near 
that temperature while the central part of the animal's body is 38 C 
warmer. 
There are other examples of this variation in tissue tempera- 
ture according to topographical anatomy as well as according to 
time. In recentworki studied a cold-acclimatized student who wears 
only a thin robe in Alaska, winter or summer. I was able to observe 
him last winter as he sat for an hour in a cold freezing room with 
only the li^t clothing that he had on when he was here yesterday. 
During much of that time, his toes and those of a colleague of his 
similarly lightly clothed remained at temperatures below ten 
degrees, and yet during that time they did not complain of pain. By 
their report of sensitivity to touch and their report of warming one 
toe as compared with another during the cyclic rewarming process, 
it was indicated that tolerance of cold was accompanied not by in- 
sensitivity but perhaps by even refined sensitivity and careful 
monitoring, both conscious and unconscious, of the thermal state in 
their tissues. 
What happens to the information system ope rating with therm o- 
labile components? I have recently been making observations on the 
detection of impact of small drops of mercury falling through a 
given distance and found that after a bit of practise I could get a 
regular threshold for the perception ofthe kinetic energy of the just 
detectable impact when my finger was at 35 C. But when the finger 
was cooled to about 22 C, the kinetic energy required to produce 
a detectable impact was elevated some five or six times. For some 
weeks in successive trials, the relation between temperature and 
threshold remained regular. 
We are thus presented with a problem incidental to thermal 
regulation which may provide a valuable clue to the nature of the 
communicating system by which animals maintain their integrity: 
how is it that the communication is effected through an extraordin- 
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