Abstract
Recent work 1 has shown that the hypothalamus plays an important part in the regulation of body temperature. In the course of a series of investigations 2 on the functions of the hypothalamus we have had occasion to make lesions in this part of the brain in the rhesus monkey (Macaca mulatta) and have kept records of the resultant changes in body temperature. Bilaterally symmetrical electrolytic lesions were made with the aid of the Horsley-Clarke stereotaxic instrument, used in the manner described elsewhere. 3 The lesions were relatively small and sharply localized. The electrode, 0.9 mm. in diameter, did very little damage on its way down through the cerebral hemisphere. In some of the animals, parts of the thalamus were involved due to the interruption of their blood supply by the more ventrally placed lesions, but these thalamic lesions were not, as a rule, extensive and varied in their location from animal to animal without any corresponding change in body temperature. Two animals, which retained normal thermal regulation, had as extensive damage in the thalamus as any of the others. Moreover, in 3 of the animals (MC 10, MC 25 and MC 26) with the most marked disturbance in temperature regulation the thalamus remained undamaged. The results to be described were, therefore, due to the lesions in the hypothalamus, the rest of the nervous system being essentially intact.
Nine of the monkeys lost the capacity to prevent the body temperature from falling below a normal level. These animals were kept for many days, in one case as long as 10 weeks, in a small room, the temperature of which was regulated at 86°F. Under these conditions these monkeys maintained a normal temperature except that sometimes during the first few days it would be slightly subnormal. If in the days immediately following the operation such an animal was removed for a few hours from the warm room to one ranging from 70° to 75°, the rectal temperature would fall rather rapidly. Gradually in the course of days or weeks these animals regained at least a fair degree of thermal control.
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