CEm'RAL AND PERIPHERAL MECHANISMS 
As a next step after panting had been established in the remain- 
ing three animals, the trunk was cooled until its subcutaneous 
temperature fell to 37 C and then reheated while hypothalamic 
temperature was kept constant at 41 C. In all three of these dogs, 
panting disappeared whenever the subcutaneous temperature fell to 
approximately 38 C and reappeared when it was re-elevated to 
41 C. The average behavior of the temperatures and respiratory 
rate during the heating and cooling cycles is shown in Figure 5. 
Therefore it appears that both central and peripheral tempera- 
tures contribute to the initiation of panting in whole body heating. 
Furthermore the difference we observed in hypothalamic thresholds 
between the series of whole body heating and of central heating was 
actually due to the absence of peripheral thermal stimuli in the 
latter. 
From these data of four Series, we are justified to conclude 
that both central and peripheral temperatures contribute to the 
initiation of thermal panting in the anesthetized dog, although the 
central mechanism is distinctly more potent than the peripheral 
mechanism. 
Subsequent questions are, then, whether such a dual mechanism 
operates also at the onset of shivering under similar experimental 
conditions during hypothermia; and if so, does it differ in shivering 
from thermal panting. 
Series V - Whole Body Cooling 
In the next series, systemic hypothermia was induced at a mean 
reduction rate of 4 C (core temperature ) per hour in 13 anesthe- 
tized animals. All the animals shivered and the average body 
temperatures at the initiation of shivering are shown in Table II. 
The hypothalamic, visceral and subcutaneous temperatures existing 
at the onset of shivering in 13 anesthetized animals were 37.3 C, 
o o 
37.5 C, and 30.0 C, respectively, and these were considerably 
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