Shivering was induced by peripheral cooling in 47 lightly anesthetized animals (10 mice, 7 rats, 9 guinea pigs, 7 rabbits, 8 cats, and 6 dogs). The mean frequency of grouped voltages in the electromyogram of the different animal groups increased with decreasing body size. The differences in the mean frequencies of the tremor between two adjacent animal groups were significant with the exception of rats and guinea pigs. These two groups differed only slightly in their mean body weight. The results suggest that the shivering frequency is dependent on body weight rather than species. No correlation was found between shivering frequency and body weight within one animal group.

On a double-logarithmic scale the relationship between the mean frequency of shivering and the mean body weight can be expressed by the following regression equation:

logy=1.85−0.18·logx

x=mean body weight (g)

y=mean shivering frequency (grouped voltages/sec).

The mean value for the shivering frequency for man, as determined from this equation, agrees well with those reported in the literature.

The mean shivering frequency decreased with decreasing body temperature.

Reflex time and contraction time measurements were done for the M. tib. anterior in 5 guinea pigs and 4 cats. The mean reflex time for guinea pigs was 4.3 msec and 7.7 msec for cats. The mean interval between muscle action potential and muscle contraction was 2.2 msec in the guinea pigs and 2.9 msec in the cats, the mean contraction time was 18.7 msec for the former, and 21.8 msec for the latter. The data suggest that the contraction time is relevant for the shivering frequency.