PHYSIOLOGY: FORBES AND RAPPLEYE 
13 
By applying the principle of Buchanan's experiments to human mus- 
cles we have obtained results which confirm her main conclusion. Elec • 
trodes connected with a string galvanometer were so appKed to the skin 
as to lead off the action currents of the first dorsal interosseous muscle 
lying close under the skin between the thumb and forefinger. Records 
were made in this way with the muscle in voluntary contraction at 
normal, subnormal and supernormal temperatures. Lowering of tem- 
perature was produced by immersing the hand and most of the forearm 
in water as cold as could readily be borne (6° to I^C)., for about fifteen 
minutes; heating was produced by immersion in water at 45°C. for a 
somewhat shorter time. By immersion to a point above the elbow 
the forearm flexor muscles were treated and investigated in the same 
way. An unmistakable and fairly marked decrease in the frequency 
of muscular action currents results from this process of chilling; and an 
increase, which, as is to be expected, is less marked, results from heating. 
As nearly as can be judged from the somewhat irregular oscillations, 
the average action current frequencies at the three temperatures studied 
were in the case of the interosseous muscle as follows : cold 39 per second, 
normal 56 per second, hot 63 per second, in the case of the forearm flexors 
the corresponding estimates are, cold 36, normal 48, hot 50. We claim 
no strict quantitative accuracy for these figures, but the uniformity of 
the estimates justifies the conclusion that there is a real change of rhythm 
correlated with change of temperature. The temperature of the body 
as a whole was shown to undergo no significant change during the 
experiments. 
The result apparently leads to the conclusion that the observed elec- 
trical muscle rhythm is not that of central innervation. It is difficult 
to conceive how a change in temperature in the muscle could alter the 
frequency of discharge of impulses from the ganglion cells whose tem- 
perature remains constant. But each propagated disturbance in a 
muscle fiber must depend on stimulation by a nerve impulse. Nerve 
impulses must therefore be so distributed in time as to render possible 
various frequencies of response such as those observed, depending on 
the temperature of the muscle. This demands a higher frequency 
of nerve impulses than that observed in the muscle rhythm. A care- 
ful study of the most perfectly rhythmical oscillations in our records 
leads us to estimate that there must be at least 300 nerve impulses 
per second to account for the muscle rhythms shown to be possible 
at various temperatures. 
Piper's strongest argument against Buchanan's view of muscle rhythm 
which we here substantiate, is that the frequency of stimuH applied 
