CLARK, G. 
The next four figures, 20, 2l,22,and23, represent some of my 
own recent work*. These are animals with rather unusual lesions. 
Routinely, extensive lesions were placed unilaterally in the anterior 
hypothalamus and contralateral to these large lesions were placed in 
the posterior hypothalamus. It was anticipated and found that such 
preparations would not present extremely grave nursing problems. 
As seen in the tests performed one month after the operation these 
cats would all be considered to have rather severe disturbances of 
regulation against heat. In this respect these cats are identical with 
those on which Ranson based much of his validation and localization 
of the dual center theory. In some of these cats even four months 
after the operation there remained a severe deficit in regulation. In 
all cases, however, the only permanent result was an increased 
panting level. In Cats 1 and 2 (Fig. 19) with the longest survival it is 
evident that this is probably a steady state defect and that no further 
improvement would have occurred; presumably this was also true in 
the others as well. A reasonable assumption would be that some sort 
of a learning process had occurred. This is negated by the fact that 
the first four animals spent most of their survival period in an air 
conditioned room in which the temperature rarely exceeded 23. 8 C 
and then only for very short periods. The animals were given short 
heat load tests at widely separated intervals. No opportunity for 
learning occurred. What then can be the mechanism for this return 
of function? In our original work the assumption was made that the 
effects of edema, etc., had disappeared by one month after the oper- 
ation. This assumption was thought to be validated by the fact that 
in cats with asymmetrical lesions there was an early loss in ability 
to withstand heat but one month postoperative responses were within 
the normal level. The assumption still seems reasonable and is sup- 
ported by the studies of Prados, Strowger and Feindel (1945). No 
explanation is in sight but one wonders what sort of an explanation 
would have been devised originally if we had continued to study our 
animals over a prolonged period of time. Of course it is probable 
that if we had waited for four months or so before testing the animals 
we would have found nothing to explain. 
•The Initial phases of this were conducted under a contract with the 
USAF 33 (616)-5657. 
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