CLARK, G. 
brain with diathermy or have cooled or heated with thermodes. In 
one of the early papers of this series (Folkow, Strom and Uvnas, 
1949) there was also confirmation of the caudal higher threshold 
portion of the heat sensitive area of Magoun. In most cases, however, 
extensive explorations were not made and in few have the anatomical 
checkups been complete or even reported. They have found it diffi- 
cult and in most cases impossible to repeat the observations of 
Magoun et aU on panting. In cats anesthetized with urethane and 
alpha chloralose circulatory responses were readily obtainable 
while respiratory responses were slight to non-existent. This diffi- 
culty, I, also can confirm for although I have been able to elicit 
panting by localized diathermic heating, more often there were no 
respiratory changes even to heating in the most sensitive area. 
Figures 9 and 10 summarize one of these papers. The area sensitive 
to local heating has a greater rostro- caudal extent and is much 
narrower ventrally than indicated by Magoun et al. (1938). Like 
Magoun et al.(1938)EliassonandStr6m (1950) used cats and inserted 
paired electrodes equidistant from the midline. As they state,the 
reactive area could very well extend further laterally than their 
figures indicate. It is worth noting that their use of two figures 
gives a good three-dimensional diagram of the reactive area. In the 
goat (Andersson, Grant and Larsson, 1956) it proved possible to 
delineate an area where mild electrical stimulation would elicit 
panting and vasodilation of ear vessels. As shown in Figure 11 the 
area is very similar to that found in the cat. Perhaps as they state 
the larger brain made possible slightly more exact localization. It 
is, of course, also true that spread of stimulus would be much less 
with electrical than with thermal stimulation. 
Figure 12 from a paper by Birzis and Hemingway (1957) would 
probably have been hailed by Hanson as convincing proof of the local- 
ization he assumed for the dual centers. Electrical stimulation (at 
points marked X) and in more caudal levels elicited shivering as 
demanded by the theory. It should be noted that after lesions con- 
fined to this particular medial region dogs have no more difficulty 
than normal dogs in combating a cold load (Keller, 1960). However, 
after much larger lesions, as shown in Figure 13, there is a severe 
damage in ability to withstand a cold load. This is shown in Figure 
14. In this test a normal dog would have a normal or slightly ele- 
vated body temperature but in the two dogs, one of whose lesions 
you have just seen, the rectal temperature dropped precipitously 
162 
