ANTERIOR HYPOTHALAMIC LESIONS 
Similarly the readjustments to pyrogen administration have only 
been perfunctorially studied. In our early studies (Ranson, Clark 
and Magoun, 1939) we had found that in cats with medial lesions in 
the anterior hypothalamus (animals which had no disturbances in 
ability to withstand cold or heat) the fever curves were markedly 
altered and there were fatal and near fatal hypothermic responses 
to pyrogens. On the other hand an occasional cat with disturbed 
temperature regulation had essentially the same responses as a 
normal animal. This is difficult to explain within the confines of the 
dual center theory for presumably animals with damage to the cen- 
tral apparatus for promotion of heat loss should have fatal hyper- 
themias to dosages of pyrogens producing only a high fever in 
normal individuals. Most of the other studies on pyrogens such as 
Chambers, Koenig, Koenig, and Windle (1949), add little knowledge 
to the field although two recent reports are of interest. Thompson, 
Hammel and Hardy (1959) reported that four hypothalectomized dogs 
failed to develop a fever following injection of a pyrogen. This was 
confirmed by Bard and Woods (1959) who found that cats with the 
brain stem sectioned at various levels between the upper mesen- 
cephalon and rostral third of the pons fail to develop a fever follow- 
ing injection of an adequate amount of typhoid vaccine. The brain 
stem of an animal similar to these (Bard and Macht, 1958) is 
shown in Figure 8. Despite the failure to develop a fever, these 
animals do show the typical transient leucopenia and other blood 
changes observable in normal animals. Both reports then indicate 
the importance of the functional integrity of the hypothalamic mech- 
anisms which enable an animal to regulate against cold in the devel- 
opment of a fever. The problem is: how is a rise in temperature in 
fever terminated in the presence of damage to the mechanisms for 
regulation against heat? 
It is also difficult to understand the maintenance of normal bocfy 
temperatures by cats with hypothalamic lesions in the relatively 
optimum temperatures of the usual animal room. If a cat is placed 
postoperatively in an incubator of 32.2 C after most lesions the 
body temperature will be normal or slightly above normal on the 
morning after the operation. However a majority of the animals 
with lesions in the heat sensitive zone will have hyperthemias, in 
some cases even above 42.2 C. Whenremovedto the animal room, 
these hyperthemias subside over 2-3 days or so and thereafter the 
body temperature remains within the normal range. However in cats 
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