NERVOUS PATHWAYS 
of superficial temperature). The threshold curve changes with the 
animal's conditions and may go up during fever (spontaneous, or 
induced by intravenous injection of vaccine). 
In normal unanesthetized dogs, with intracerebral thermo- 
couples, ingestion of one liter of ice water induces a rapid fall of 
central temperatures with much shivering, even whenthe superficial 
temperature is kept hig^. Shivering disappears when the central 
temperature comes back to the normal level. 
Finally, cold exposure on the thermal equilibrium can be com- 
pensated for by heat production of the muscular work that is exper- 
imentally imposed on the organism. There are two possibilities in 
this case. The autonomic thermogenesis of the organism may be 
regulated by the superficial stimuli; this thermogenesis would thus 
add to the heat production of the work. If the regulation is made by 
the need of constancy of central temperature, which is almost 
accomplished, there is substitution. We have shown that, in spinal 
dogs, the muscular work induced in muscles of the hind legs by 
electric stimulation increases the oxygen consumption only in neutral 
ambient temperature. In the cold, this consumption replaces the 
need for oxygen which is induced by cold, but does not increase it. 
Direct cooling of the central nervous system 
We implanted aseptically and stereotaxically in the brains of 
eleven dogs a thermode producing cold by gaseous detent of propane. 
The central temperature near the thermode was registered with a 
thermistor at the same time as the rectal and three or four super- 
ficial temperatures. The electromyograph was recorded in the awake 
dog with an ink-writer, with or without integration (Figs. 9 and 10). 
Results show that there is a close correlation between the cen- 
tral temperature and the electromyograph. Every decrease of the 
cerebral temperature is associatedwith an increase of the muscular 
tone or even with a clear-cut shivering. The most striking results 
are obtained when the thermode is located at the middle hypothal- 
amus. In such a case, only a decrease of 1/10 degree centigrade is 
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