NERVOUS PATHWAYS 
by muscular activity by cuttingmotor nerves to an extensive region. 
This procedure pointed out the persistence of a potent increase of 
heat production against cold. But the active portion of the muscula- 
ture can still be responsible for that result. 
Lesions of the spinal cord have been attempted also, though 
they are less specific in their meaning. According to Freund (1913), 
section of the thoracic cord in the rabbit abolishes the whole phys- 
ical regulation against cold, leaving the chemical regulation un- 
changed or even more active in compensation. Kayser (1929), 
experimenting on the pigeon, observed similar results after section 
of the thoracic cord. Hermann, (1938), using the dog, saw the per- 
sistence of an efficient regulation against cold after destruction of 
the cord below thoracic one level. In cold ambient temperature, 
there is a distinctly greater increase of heat production in the same 
animal species we have seen than in the dog before the lesion. The 
maximum metabolism is not yet reached at -15 C, and the curve of 
metabolism is still ascending at this temperature despite extensive 
paralysis and the lack of epinephrine secretion. In that preparation, 
of course, a part of the musculature remains active and seems to 
be able to compensate for exaggerated heat loss in the cold. Indeed, 
in absence of vasomotor regulation, the heat production has to 
balance more exactly the thermal demand of the environment and 
any deficit must appear unmasked. 
Issekutz (1937) found that cervical section of the dog reduces 
the thermogenetic responses in the cold. According to Freund (1913), 
rabbits then become poikilothermic. These authors explain these 
results by the assumption of the suppression in that section of 
important vegetative outflow leaving the cord at this low cervical 
level. Our results confirm that section or destruction of the cord 
reaching the inferior cervical segments seriously disturbs the 
chemical regulation in the dog. In the cold, below -10° C, a maximum 
metabolism level of 2 to 2.5 times the basal value is reached with 
fall in central temperature, but there is no complete poikilothermia. 
Besides, we think that the difference between cervical and thoracic 
lesions can be explained more properly by the motor outflow of 
the brachial plexus at this level. 
In order to test this explanation, we tried to ascertain the role 
of the cervical and brachial plexuses in the potent thermogenetic 
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