HEMINGWAY, A. 
Electromyogram. The shivering muscles, which are under- 
going contraction and relaxation, produce action potentials which 
can be amplified and recorded on kymograph paper. The electro- 
myograms as recorded with an AC amplifier consist of a suc- 
cession of biphasic spike potentials, irregular in frequency and 
amplitude. Using a suitable rectifier, these biphasic potentials can 
be converted into an integrated monophasic record whose ampli- 
tude is roughly proportional to the intensity of shivering. 
The thermal cutaneous vasomotor response. The ability of the 
cutaneous vessels to constrict in the cold and dilate in the heat 
can be measured conveniently in dogs by measuring their ear skin 
temperature. In a cool environment of 15 to 20 C, cutaneous vaso- 
constriction is indicatedby a low ear skin temperature of 2 to 3 C, 
above environmental temperature. Vasodilation, in this environment, 
caused by central or peripheral heating, is indicated by a rise in 
the ear temperature which will reach values as high as 34 C. 
This test is simply an indicator of cutaneous vasoconstriction and 
vasodilation, and is roughly quantitative. 
Other methods of measuring cutaneous blood flow are the (a) 
photoelectric plethysmograph (Hertzman, et al., 1946); (b) the 
impedance plethysmograph (Nyboer, 1960); (c) the venous occlu- 
sion plethysmograph (Abramson, 1944, and Freeman, 1945); and (d) 
the opening of a cutaneous vein and measuring the blood flow rate 
of the blood lost by hemorrhage. The photoelectric plethysmograph 
and the impedance plethysmograph cause negligible discomfort to 
the animal or human subject, but the measurements are only approx- 
imate. The venous occlusion plethysmograph, while it gives quant- 
itative values of blood flow rate, does not measure cutaneous blood 
flow alone, but the blood flow of the extremity. The assumption is 
required that the venous occlusion obstructs all of the venous out- 
flow from the extremity and does not interfere with arterial in- 
flow. The measurement of the cutaneous blood flow by hemorrhage 
is suitable only for animals under anesthesia. 
