CENTRAL AND PERIPHERAL MECHANISMS 
METHODS 
To meet the necessary requirements which are described above, 
it was necessary to use the anesthetized preparation. The mongrel 
dogs were anesthetized with barbital sodium with or without morph- 
ine sulfate. In some series chloralose was also used. The use of 
anesthesia has its advantages and also its disadvantages. On the side 
of advantages, it eliminates one of the sources of ambiguity, namely, 
the panting or shivering responses due to so-called conditioned 
reflexes. Barbital sodium is one of the long- acting barbituates and 
our preliminary study indicates that a stable background of normal 
blood pressure and respiration can be maintained for more than 8 
to 10 hours following a single dose of this reagent. On the side of 
disadvantages, of course, it is well known that the barbiturates de- 
press the thermoregulatory mechanisms. However, this disadvan- 
tage is minimized by using the minimum amount of anesthesia 
necessary for the surgery. 
Body temperature was measuredby means of copper-constantan 
thermocouples soldered into hypodermic needles. In the study of 
thermal panting, the hypothalamic thermocouple was inserted 
through a trephine opening in the parietal bone. The angle and depth 
of insertion required to reach the desired area were determined 
previously by measurements on the brains of dogs of similar 
size. We used the medium size of dogs. The position was checked 
at post-mortem in each experiment, and was found to be within the 
thermosensitive area described by Magoun and his co-workers 
(1938). This technique of parietal approach, however, is rather time 
consuming. Therefore, a simple method of orbital approach was used 
in the study of shivering. The latter technique consists of implanting 
a thermocouple through an orbital fissure or optic foramen, into 
the hypothalamic region. In dogs these cranial openings are rela- 
tively large and straight. The hypothalamic, esophageal, gastric, 
and rectal thermocouples served as core temperature sensing ele- 
ments. Four oher thermocouples were inserted subcutaneously in 
front and hind legs and in the anterior and lateral abdominal walls. 
81 
