LIM, T. P. K. 
Series I - Whole Body Heating 
I shall describe the heat experiment first and then the cold 
experiments. In the first series, 10 animals were heated in the 
cabinet for an average period of 3 hours, and, as we anticipated, 
all 10 animals panted. The average hypothalamic, subcutaneous, 
and rectal temperatures at the onset of panting are presented in 
line 1 of Table I. The mean preheating control temperatures were 
37.2 C, 36.1 C and 37.0 C for the hypothalamus, the subcutaneous 
tissues and the rectum, respectively. Since both central and peri- 
pheral temperatures rose significantly, it is impossible to decide 
whether one or the other or both were responsible for the initiation 
of panting. Since individual animals were heated at different rates 
^ o o o o 
(cabinet temperatures of 31 C, 34 C, 37 C, 41 C) and control 
temperatures varied over a considerable range (34 C to 40 C), 
the datawereanalyzedtodetermine whether the temperature thresh- 
olds for panting varied with the control temperature or heating 
rate. No significant correlations were found. 
Thus, when the whole body of the barbitalized dog is heated, 
panting occurs when both central and peripheral temperatures are 
in the neighborhood of 41 C. These temperature thresholds are 
independent of both control temperature and rate of heating within 
the range studied. 
Series II - Peripheral Heating 
In the next series we wished to determine whether "pure peri- 
pheral panting" could be produced or not. Therefore, the trunks of 
four anesthetized dogs were heated in the cabinet at temperatures 
between 45 C to 50 C for 3 hours, while their hypothalamic 
temperatures were kept between 36 C to 38 C by carotid cooling. 
Panting did not occur in any of the animals, the respiratory rate 
increasing from a mean control value of 24/min to only 46/min at 
the end of the heating period. The average maximum temperatures 
reached at the end of the heating period are summarized in line 2 
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