CLARK, G. 
DISCUSSION 
DR. STUART: Do you have the histology of the animals that 
were shown in the last two slides? 
DR. CLARK: I do not have them with me, but the lesions were 
virtually unilateral hem isections. They were good, big-sized lesions. 
DR. FREEMAN: Since this question of the compatibility of my 
data with the dual center hypothesis came up, I might say that we 
were trying to prove this hypothesis when we started off with this 
work in 1950, with the idea that there was a cold center posteriorly 
and heat center anteriorly. If you stimulated them with conductive 
thermal changes, you should get appropriate activation of a mech- 
anism for heat loss by heating the anterior hypothalamus, and 
nothing if you cool. You should get opposite effects with the poster- 
ior hypothalamus. What we found was, as you see, that sensitivity 
to both heat and cold could be demonstrated to exist anteriorly and 
that the inverse changes took place in the posterior hypothalamus. 
This sent me back to Hanson's original description of this hypoth- 
esis, and it struck me then — and it does so now — that there was a 
peculiar confusion or ambiguity in his expression of this thing. He 
described heat loss mechanisms or centers in the anterior hypo- 
thalamus and in the posterior hypothalamus and did not specify 
whether these were sensory or motor or both. He never said, as we 
thought he had said, that these were heat- sensitive and cold- sensitive 
mechanisms. He was simply describing his results in more general 
terms without specifying as to whether temperature sensitivity 
exists in either one of these areas. 
DR. CLARK: At that time, it was thought that the work with the 
diathermy had conclusively proved that the region beneath the an- 
terior commissure was a heat-sensing area, but we had no data 
whatsoever about a cold sensing area. The only thing we had was the 
fact that the caudal and lateral hypothalamus lesions produced ani- 
mals that could not withstand cold as well as normals; those lines 
he drew were entirely hypothetical. 
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