KIM, T. P. K. 
o 
lower than those of the precooling control period, which were 37.9 
C, 38.1° C and 33.2° C, respectively. Since both central and peri- 
pheral temperatures were reduced significantly, it is impossible 
to differentiate whether one or the other or both were responsible 
for the production of shivering. 
Ser ies VI - Central Cooling 
In the next series, we wished to determine whether central 
shivering could be produced. Therefore, the brain temperature 
alone was gradually lowered in seven animals by cooling the caro- 
tid blood over an average duration of 35 minutes (range: 15 to 55 
min). All animals began to shiver on the average within 15 minutes 
(range: 5 to 30 min) at a brain temperature of 36.2 C (Table II). 
Note that on the average the cerebral temperature was reduced 
from 38.0 C to 36.2 C, while the visceral and surface temperatures 
were maintained at practically the same levels as in the control 
period. A comparison of the hypothalamic temperature thresholds 
for shivering in whole body cooling and those of the central cooling 
indicates a significant difference (p<0.05), the latter being markedly 
lower than the former. From this series it is concluded that central 
shivering can be produced in the anesthetized dog, but that the 
hypothalamic temperature threshold is lower in central than in 
whole body cooling. 
In the genesis of central shivering in our preparation, one might 
suspect that peripheral thermoreceptors in the head, such as are 
known to exist in large number in the facial region supplied by the 
trigeminus nerve, particularly might have contributed Sv": me periph- 
eral stimuli for shivering. This is one of the criticisms against 
this t}TDe of cooling or heating experiment. To explore the role of 
these receptors, a thermocouple was implanted in a nostril and an 
electrical heating tape was wound around the mouth and the ncse. 
Central shivering was produced by lowering the brain temperature 
and the tape was warmed until the nostril thermocouple registered 
an average of 44^^ C, the mean heating duration abcve 40 C being 
6 minutes. None of three animals so treated ceased v: shiver, ncr 
did the muscle potentials of shivering diminish. Thus it is most 
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