NERVOUS PATHWAYS 
However, the existence of a central sensitivity towards the 
cold is still in question. Numerous attempts to demonstrate this 
sensitivity are negative, according to the work of Strom (1950), 
Forster et al. (1952), and Brendel (1960);sucha central mechanism 
is sometimes judged useless since, on exposure to cold, the im- 
mediate reaction is an increase of the core temperature. Positive 
results of Barbour (1912) are criticized because of the tremendous 
lowering of braii;i temperature required for the experiment. 
Since 1954, we have made several approaches to this problem, 
in order to know whether chemical regulation and particularly 
muscular activity and shivering can be put into action by a central 
action of the cold. At the beginning of this work we tried to obtain, 
by several means, a shift in the normal temperature gradient of the 
bocfy. Thus, the internal bocfy temperature might decrease (in order 
to trigger any central sensitivity) but the superficial skin tempera- 
tures would remain constant or even increase (in order that super- 
ficial cold receptors would not be stimulated). 
Experiments were performed systematically onunanesthetized 
dogs bearing chronically implanted thermocouples in the brain; 
several subcutaneous temperatures were also registered. Shivering 
and muscular tone were registered by electromyograph, and some- 
times by respiratory exchanges. 
In a chronic spinal dog, or in a dog whose spinal cord is des- 
troyed up to thoracic one level, central cooling may be induced by 
wrapping ice bags around the posterior part of the bocfy which is 
deprived of sensitivity. In such a case, warm blankets and infrared 
lights induce a warmer temperature on the anterior part of the 
body and particularly on the face. In other cases, for reflex cold 
stimulation, the face could be refrigerated. 
The results may be summarized as follows on a graph (Fig. 8): 
on the ordinate is central temperature; on the abscissa is mean 
superficial temperature. It is possible to show the existence of a 
"shivering zone" above a threshold curve. Thus, during the same 
experiment, shivering may be induced by the decrease of super- 
ficial temperature (with a constant central temperature) or by a 
decrease of central temperature (with no change or even an increase 
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