HISTORICAL REVIEW 
be essential for homeothermy. However, the Fort Knox workers, in 
contrast with earlier workers, were able to keep their animals 
alive for many months and make homeothermy tests long after the 
traumatic shock of the operation had subsided. 
The most popular technique for producing localized lesions in 
the central nervous system has beenthe electrolytic lesion produced 
at the tip of electrodes placed in the brain of anesthetized animals 
from the Horsley- Clark head frame. With this procedure, it is 
possible to make a lesion of a desired size at any desired location 
within the brain. The cat is the animal of choice for these studies 
due to the uniformity of the size and shape of the head. The first 
study of impairment of temperature regulation caused by these dis- 
crete lesion was made by the Ranson school of investigators. The 
earlier work of this group has been reviewed by Ranson in his clas- 
sical 1940 paper. Examples of the type of lesion made by this method 
from work of Birzis and Hemingway are shown in Figure 5. In this 
figure, the regions of the brain destroyed are small areas in the 
lateral pons with the level of the section being shown in the upper 
half of the figure. This lesion abolished shivering in a cat. The 
advantage of this method of producing a lesion over the transection 
and puncture technique is that regions remote from the brain sur- 
face can be destroyed with little injury to surface structures. 
Using the Horsley- Clark method of producing bilateral lesions 
at different levels in the brain stem of the anesthetized cat, Birzis 
and Hemingway (1956) have found that a region of the brain stem 
essential for shivering comprises a long pathway extending from 
the posterior hypothalamus to the medulla. This pathway starts 
downward from a position just dorsal to the junction between the 
medial edge of the cerebral peduncle and the lateral border of the 
mammillary bodies. As it descendsthroughthe midbrain, it courses 
dorsolaterally to the red nucleus, and in the pons it deviates later- 
ally, reaching a superficial position immediately adjacent to the 
transverse pontine fibers. It retains its lateral position in the upper 
medulla. This pathway through the brain stem is shown in Figure 
6. The pathway consists of the region within the elliptical figure 
drawn on the sections. It will be noted that this pathway does not 
involve the corticospinal tracts. Figure 7 shows the site of lesions 
which destroyed the corticospinal tracts and adjacent areas of the 
17 
