CENTRAL AND PERIPHERAL MECHANISMS 
subcutaneous and rectal temperatures remained at low levels 
whereas hypothalamic temperature was considerably elevated. 
Comparing the mean temperature thresholds for panting in the 
present series with those of Series I, we note that the hypothalamic 
threshold is 1.5 C higher in the former, and this difference is 
statistically significant (p<0.01). Two animals of the present series 
failed to pant even thoughtheir hypothalamic temperatures exceeded 
43° C. 
From these results, we infer that "central panting" can be 
produced in the anesthetized dog, but that the hypothalamic temper- 
ature threshold is higher in central heating than in whole body 
heating. This implies, then, that both central and peripheral tem- 
peratures contribute to the initiation of panting in whole body heating. 
It is considered likely that hypothalamic rather than head skin 
receptors played the mahor role in the "central panting" of this 
series, although some contribution from the latter is probable. 
Series IV - Termination of Panting by Central or Peripheral 
Cooling. 
If it is true that both central and peripheral temperatures 
contribute to the initiation of panting in whole body heating, then 
panting established by simultaneously raising both temperatures 
should disappear whenever either one alone is lowered to a lower 
level while the other is kept at its "whole body threshold." In the 
next series, panting was established in seven anesthetized dogs by 
simultaneously heating the head (by carotid warming) and trunk 
(in the cabinet). In four of the animals, hypothalamic temperature 
o o 
was then lowered to 37 C and re-elevated to 41 C repeatedly 
while trunk temperatures were kept nearly constant at high levels. 
In all four animals, panting stopped whenever hypothalamictempera- 
ture fell to approximately 38 C to 39 C and reappeared when the 
latter was re-elevatedto 41 C. The average behavior of the temper- 
atures and respiratory rate of these four dogs during the heating 
and cooling cycles is shown in Figure 4. 
89 
