NERVOUS PATHWAYS 
sufficient to trigger a muscular response. These reactions are ob- 
tained even with a constant superficial temperature; nevertheless, 
the superficial temperature has some effect on the amplitude of the 
muscular reaction induced by cold central stimulation. 
These results agree with those of Hammel, Wyndham, and 
Hardy (1958), who obtained shivering by local cooling of the dog 
hypothalamus. Freeman and Davis (1959) and Kri^er et al. (1959) 
were also able to register vasomotor reactions in the cat to cold 
acting in this region. Donhoffer et al. (1957), cooling the brains of 
rats, observed an increase of heat production. 
Lim (1960), from experiments in cooling carotid blood in the 
dog, concluded that shivering can be elicited either peripherally or 
centrally. In this respect, negative attempts can re suit from the use 
of anesthesia, from the operative shock, or from defective localiza- 
tion of the thermode, in consideration of the strong convection in 
the brain. 
Exclusion of central sensitivity. Chlorpromazine does not de- 
crease the capacity of resistance against cold in a normal animal. 
A dog treated with chlorpromazine in a cold environment may shiver 
normally and increase its therm ogene sis, and may be used as a 
control animal. But the hypothermic dog (spinal dog overstrained 
by a cold environment) given chlorpromazine, does not react against 
cold and stays hypothermic if there is no superficial stimulation, 
that is, if superficial receptors are submitted to a high ambient 
temperature by heating. But such a dog may shiver and its rectal 
temperature may increase when it is surrounded by a cold ambient 
temperature. This paradoxical behavior can be explained by a selec- 
tive suppression of the central component of the thermal sensitivity 
to cold by chlorpromazine. 
We performed electrolytic destruction of the hypothalamus in 
nineteen dogs. In several of them we obtained thermoregulatory be- 
havior resembling that of chlorpromazine. Such animals recover 
some reactions against cold post-ope ratively, such as increase of 
thermogenesis when placed in a cold ambient temperature, but this 
reaction does not permit an exact adaptation of the heat production 
to the loss. The central temperature remains unsettled and there is 
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