NEURO-MUSCULAR ORGANIZATION OF SHIVERING 
Second . Shivering is more intense in jaw muscles when the head 
of the dog is in the normal horizontal position. In this position, the 
anti-gravity jaw muscles are subjected to more tension with a con- 
comitant increase in proprioceptive activity. 
Inhibitory Considerations 
These results suggest the following concepts relating to inhib- 
itory shivering mechanisms: 
First . Uprus et al (1935), using unanesthetizedhuman subjects, 
have shown that shivering ceases as the rectal temperature rises 
and reoccurs as the temperature falls, even in the presence of a 
hi^ initial temperature. The results on anesthetized animals would 
suggest that shivering can be both inhibited by radiant heating and 
instigated by cold air without any change in rectal temperature. 
Shivering was inhibited in low rectal temperature dogs when the 
backs of the animals were briefly heated. This phenomenon may be 
due to a sudden increase in excitatory impulses to the anterior hypo- 
thalamic inhibitory region from dorsal heat receptors. Such a brief 
and sudden input could be sufficient to inhibit shivering temporarily. 
Unfortunately, it is not known if such inhibition mig^t be only 
temporary in the face of consistent low blood temperature since the 
period of radiant heating was of short duration. At any rate, this 
phenomenon is a clear example of a peripheral stimulus antagonizing 
the physiological effects of a contrary central stimulus. 
Second. In deep anesthetic states a noxious stimulus can facili- 
tate shivering. But in light anesthetic states noxious stimuli tend to 
inhibit shivering, even when the blood temperature is below normal. 
This type of inhibition may be due to the noxious stimuli evoking 
avoidance behavior in the animal and as such voluntary avoidance 
movements would tend to inhibit shivering by sucpessful seizure of 
the motor neuron pool. Such a concept is supported by Stuart, Free- 
man and Hemingway's unpublished findings that restraint devices 
inhibit shivering in unanesthetized chilled cats. It is difficult to ac- 
count for the earlier appearance of shivering in tongue, jaw, and neck 
muscles than in limb muscles. At first glance it appears analogous 
to the development of tetanus and tetany. However, restraint and 
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