HEMINGWAY, A. 
would serve to explain the existence of a widely distributed shiv- 
ering suppression mechanism which can be immediately initiated 
when needed. 
Recording of electrical activity. A new tool in electrophysiol- 
ogy which has been used rather extensively in the last 10 years is 
the use of microelectrodes and semi-microelectrodes for recor- 
ding of electrical activity of the cells of the central nervous system. 
These electrodes have a diameter of from 0.2/i to 50m and are, in 
diameter, of the same order of magnitude as nerve cells and their 
processes, i.e., 0.5iJ. to 20/i. When placed in contact with a nerve 
cell (or nerve fiber) which is actively functioning, the electrical 
of the cell is transmitted to the electrode (Freeman and Hemingway, 
1959). The electrical potential of the active cell consists of a series 
of rapid transient potentials called "spike" potentials. These poten- 
tials are amplified and transmitted to a cathode ray oscilloscope 
and photographed. Birzis and Hemingway (1957) were the first to 
record well defined spike potentials associated with shivering. 
These potentials appeared with shivering and disappeared with 
cessation of shivering. Records of these potentials are shown in 
Figure 9. These potentials were recorded from electrodes placed 
on the "shivering pathway" whose boundaries were determined by 
lesion experiments as described earlier in this paper. A semi- 
transection made just caudal to the point from which the potentials 
were recorded did not prevent or change these spike potentials 
(see Figure 10). This is evidence that the potentials were action 
potentials of fibers carrying shivering impulses downward in the 
central nervous system to lower motor neurons, that is, they were 
part of the efferent fiber system controlling shivering. These spike 
potentials associated with shivering were extensively studied by 
Freeman and Hemingway (1959), who found that the action potentials 
could be recorded from the "shivering pathway" previously des- 
cribed and extended from the fields of Forel in the posterior hypo- 
thalamus to the olive in the medulla oblongata. By using a high 
amplification and rapid sweep of the cathode ray oscilloscope, a 
characteristic change of potential pattern was discovered in prece- 
ding from the fields of Forel to the olive, which permitted a tentative 
interpretation of these potentials (based on a theory proposed by 
Lorente de No) as spike potentials travelling downward in the brain. 
There were, however, two disturbing factors of this study. The 
impulses seemed to arise from the fields of Forel and travel down- 
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