HISTORICAL REVIEW 
of a particular function. However, the site of injury is extensive 
and excessive loss of function occurs. In recent years, most of the 
investigative work seeking to understand the extent and activity of 
various regions of the central nervous system has consisted of 
making small discrete lesions and testing the animal before and 
after the operation to determine loss of function caused by the lesion. 
In the older work, the puncture technique was used. This con- 
sisted of first exposing the surface of the brain, inserting a probe 
or small scalpel, and destroying mechanically from the surface 
inward, a region adjacent to tne surface. This was the method used 
in the classical work of Isenschmid (1912, 1914), whose work first 
definitely localized within the hypothalamus, the control for temper- 
ature regulation. The anatomical site of lesions in the brains of 
rabbits produced by the puncture technique of Isenschmid is shown 
in Figure 4. The stippledareas of the brain cross-sections represent 
the regions destroyed by the puncture. The clear unstippled areas 
represent intact brain. Below each of the four sections of Figure 4, 
the interference with homeothermic function caused by the lesion is 
indicated. In the section designated "abolished", there was no 
temperature regulatory function - the animal was poikilothermic. 
In the section labeled "undisturbed", temperature regulation was 
normal. If one superimposes the "undisturbed" section in the lower 
left-hand corner over the "abolished" section of the upper right- 
hand corner (since both of these sections are at the same level), 
it will be found that a small region in a transverse plane at the 
caudal border of the mammillary bodies, dorsolateral to the mam- 
millary bodies and at a position laterally about one-fourth of the dis- 
tance from the wall of the third ventricle to the lateral surface, 
must be intact and have neural connections with more caudal portions 
of the central nervous system for maintenance of homeothermy. 
The role of this particular region in temperature regulation will 
be discussed later in the Symposium by Douglas Stuart. In more 
recent years, a similar technique has been used by the neurophy Bi- 
ologists of the Army Medical Research Laboratory at Fort Knox, 
particularly Keller and Batsel (1952) and Keller (1956). Using elec- 
trocoagulation, a region of the brain was destroyed which resulted 
in converting a dog to a poikilothermic state (or nearly poikilo- 
thermic), producing a preparation called the "poikilothermic dog'". 
The region destroyed was at the junction of the mesencephalon and 
diencephalon and included the region found earlier by Isenschmid to 
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