LIM, T. P. K. 
produced in three animals (Table III), the hypothalamic temperature 
being maintained between 34 C to 37 C. This was followed by 
° 
warming the animal's trunk (water temperature =40 C to 45 C) 
to examine whether such a thermal counteraction on the part of the 
periphery could suppress central shivering. All three animals 
ceased to shiver within 1 to 2 minutes of peripheral warming at a 
mean surface temperature of 34.9 C. Utilizingthe same preparation 
the procedure was reversed. This time, peripheral shivering was 
produced by surface cooling and then central warming was initiated 
to 1-ist whether the opposing temperature on the part of brain center 
could arrest peripheral shivering. All three animals ceased to 
shiver after 10 to 28 minutes of central heating at an average brain 
temperature of 41.5 C. 
From the results of these cooling experiments (Tables II and 
III), it is inferred that shivering can be produced by differential 
cooling of the head or the trunk alone as well as by whole body 
cooling, but the peripheral mechanism of shivering is very potent. 
o 
In the studies of thermal panting, peripheral heating up to 45 C 
(brain temperature, 36 G to 38 C) did not produce panting in dogs 
under either barbital sodium orchloralose anesthesia. In the studies 
o 
on shivering, however, the reductionof skintemperature from 33 C 
to 30 C while maintaining a brain temperature of 38 C invariably 
produced a shivering response. This distinctive difference in the 
roles of peripheral stimuli in shivering andthermal panting leads us 
to conclude that, in general, the the rm al inf lax from the peripheiy in 
the cold plays a more dominant role than in a wami environment. To 
elucidate further, the relative importance of central andperipheral 
thermal stimuli in the initiation of thermal panting and shivering, the 
hypothalamic and subcutaneous temperature thresholds for panting 
and shivering are plotted in Figure 6. The open circles indicate^ 
temperature thresholds for panting and the closed circles those for 
shivering in whole body as well as regional heating and cooling ex- 
periments. The trend of the two curves is shown by the freehand 
drawings (Fig. 7) which are designated as the iso-panting and the 
iso-shivering line, respectively. It appears that the slope of the iso- 
shivering line is much steeper than that of the iso-panting line, 
which suggests that at a fixed level of brain temperature, the alter- 
ations in the skin temperature play a more significant role at the 
onset of shivering than thermal panting. Conversely at a fixed skin 
