LIM, T. P. K. 
DR. CLARK: Well, the chief thing is, of course, that with an 
increase in amplitude you are primarily getting a ventilation of the 
dead space, which is implied in the term "panting". Actually, I have 
seen cats panting at temperatures below 38 C. 
DR. HEMINGWAY: I have studied panting in both anesthetized 
and unanesthetized dogs and I agree with Dr. Clark; there is an 
abrupt change in the respiratory pattern when an animal pants. It 
is quite different from the hyperventilation that you get, say, with 
the decerebrate animal. It is possible just by raising the tempera- 
ture of a cold-blooded animal and warm blooded animals that have 
been made poikilothermic by decerebration to get this hyperpnea 
or hyperventilation, but the normal animal without anesthesia has 
a distinct change in pattern. There is a drop in tidal volume which 
is very striking. I do not think you can really tell with an anesthe- 
tized animal whether heispantingornot; it is so different from that 
of the unanesthetized animal. In the former you can have hyperven- 
tilation or h)T5erpnea, but it is difficult to say when you have panting. 
With an unanesthetized dog, it is very easy. 
DR. JOHANSEN: Is it conceivable that the vascular changes in 
the brain produced by your cooling of the carotid blood could bring 
in another stimulus that could interfere with the temperature, 
per se ? 
DR. LIM: I did not mention it in detail, but we did obtain some 
data on the threshold levels with whole body heating in intact 
animals, without any insertion of coils into the brain circulation. 
In other experiments with repetitive heating or cooling, we produced 
panting by simultaneous heating of the brain and the skin. There 
was no statistical difference between the results of these experi- 
ments as far as thresholds are concerned. This would indicate that 
the disturbance of the cerebral circulation by insertion of the coil 
may not be a major problem. 
DR. JOHANSEN: To the best of my knowledge, the internal 
carotid is the main supply to the tongue of the dog. So, although 
you warm the nostrils and the skin of the face, you might also have 
an input from the tongue. 
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