138 ELECTRO-PHYSIOLOGY CHAP. 



stimulation-frequency, since the tone produced is an octave, a fifth, or 

 even two octaves lower. According to Wedenski there is complete 

 parallelism between the electrical oscillations and the mechanical 

 (audible) vibrations of the muscle, in the sense that the pitch of 

 both tones is identical. The muscle responds to each very 

 frequent excitation by a characteristic bruit, but not by a tone of 

 corresponding pitch. The limit in warm-blooded muscles lies at 

 about 1000 stimuli per sec.; in frog's muscle it is much lower: 

 according to Wedenski this last ceases to give a tone corresponding 

 with the stimulation -frequency at about 200 stimuli per sec. 

 Loven usually failed in hearing any mechanical tone (caused by 

 vibrations) in the gastrocneniius of the frog, even with the help of 

 the most sensitive instruments. This seems to indicate that the 

 capacity of muscle to produce a musical tone in response to 

 rhythmical excitation is the more developed in proportion with 

 the mobility of the muscle, i.e. with the rate of its contraction. 

 (Birds' muscles would presumably respond to very high frequencies: 

 the pale muscle of mammals, according to Kronecker and Stirling, 

 I.e., far surpass the red in this particular ; tortoise muscle emits 

 hardly any sound, or only at a comparatively low frequency.) It 

 also appears that the capacity of a muscle to give out sound 

 suffers considerable variations if the mobility of the smallest 

 particles is from any cause diminished. This specially applies 

 to fatigue, to which is owing the fact that a muscle which, at the 

 beginning of excitation, gives out a tone of corresponding pitch, 

 subsequently produces a deeper sound, and eventually only an 

 indefinite murmur (Wedenski, I.e.} Finally, the character of the 

 muscle-tone depends also upon intensity of the single stimuli : 

 where this is very low an undefined murmur replaces the musical 

 tone at maximal excitation, in spite of an adequate stimulation- 

 frequency. 



The fact that the muscle-tone does not always correspond 

 with the frequency of stimulation in direct excitation from the 

 nerve, makes conclusions as to the rhythm of central innervation, 

 deduced from the ntnr.l muscle-bruit, very uncertain. We have 

 said above that muscles, when thrown voluntarily into vigorous 

 and persistent contraction, emit a dull, humming sound. It is 

 difficult to determine the pitch of the ground-tone in this case, 

 because it lies on the threshold of perceptible tones. Helmholtz 

 estimated it in his masticatory muscles at :>("> 40 vibrations 



