HISTORICAL REVIEW 
by steel wires but hinged to the fixed platform. When shivering 
starts, the movable platform vibrates, andthe vibration is recorded 
to give a mechanical record of the tremor of shivering. The head 
of the dog is sealed within a chamber through which gas of the 
closed respiratory system is circulated with an airtight pump (re- 
frigerator pump). Respiration and oxygen consumption rates are 
recorded from a spirometer of the closed circuit system. Thermo- 
couples are used to record skin and rectal temperatures. Electrodes 
sealed to the skin with collodion areusedfor recording of the elec- 
tromyogram. Trained animals will lie for as long as 3 hours in this 
apparatus and endure cold sufficient to produce shivering without 
attempting to move. A record of the start of shivering as revealed 
by the record of rectified action potentials is seen in Figure 2. 
Before shivering, there was slight background electrical activity 
due to respiration and the heart beat. When shivering started there 
was a sudden rise in the rectified action potentials which was coin- 
cident with the appearance of visible shivering. For this animal, 
there was no increase of electromyographic activity preceding 
visible shivering. 
The apparatus used in studying shivering in cats is shown in 
Figure 3. A cat is not capable of being trained to lie in a relaxed 
resting condition such as is a dog. A carefully selected cat will, 
however, sit with little voluntary movement for an hour or two in 
a confined box such as is shown in Figure 3. The cat sits on a 
platform supported by springs or rubber stoppers and shivering 
is recorded by a strain gauge attached to a movable platform. The 
box which contains the cat is sealed airtight and the gas within the 
box is circulated by means of a sealed pump. The box having a glass 
cover is placed within a refrigerator, also with a glass cover, so 
that the cat can be observed. The gas of the enclosure is circulated 
through cooling coils immersed in ice water in the refrigerator. 
Continuous analyses are made of the O and CO content of the 
enclosed gas. This apparatus permits a measurement of oxygen 
consumption rate, but not a measurement of respiration. Thermo- 
couples and electromyographic electrodes record temperatures 
and muscle action potentials respectively. 
