i GENERAL PHYSIOLOGY OF MUSCLE 21 



36-40 vibrations, while the natural vibration of the human muscles is 

 only 18-20 per second. Similar results were obtained by Kronecker 

 and Stanley Hall (1879), who registered the oscillations in the 

 mass of the exposed femoral biceps of the rabbit by applying the 

 lever of a Marey's tambour to its surface, and tetanising the spinal 

 cord with an induced current of 43 shocks per second (Fig. 13). 



Later work on this subject, particularly by Loven, von Kries, 

 Schafer, Wedensky, and Stern (1900), however, yielded different 

 and apparently contradictory conclusions in certain particulars, 

 while confirming the fact that all voluntary contractions, and 

 those due to strychnine and to reflex or direct stimulation of the 

 cerebral centres, are discontinuous phenomena, i.e. are due to the 

 summation of a series of impulses emanating from the centres and 

 transmitted to the muscles. 



It is difficult on the generally accepted theory of Helmholtz, 

 that the sound heard from a muscle either in tetanus or in per- 

 sistent voluntary muscular contraction depends essentially on the 

 displacement of the contractile substance, to explain the fact that 

 simple twitches or contractions, such as the cardiac systole, can 

 give rise to a murmur. 



Lastly, it should be added that Briinings (1903) made an 

 accurate analysis of the muscle sound ' produced by direct and 

 indirect stimulation with faradic currents of varying frequency. 

 He found that it always has the character of a simple tone, and 

 that its frequency never differs from that of the stimulus. But if 

 on direct stimulation the frequency of the faradic currents is 

 constantly increased, the intensity of the muscle sound grows 

 proportionately less, until it disappears altogether after reaching a 

 certain limit of frequency, though the tetanus still continues. 

 This maximal limit is higher in proportion to the strength of the 

 stimulus and the freshness and the temperature of the muscle. 

 Its relation to the temperature in particular is surprisingly 

 regular. While, e.g., at 7'5 C. 3 stimuli per second is the maximum 

 at which an isorhythmic murmur can be obtained, no sound being 

 heard at any higher frequency, at 35 C. the highest perceptible 

 tone is observed with 435 vibrations. 



IV. To complete the analysis of the mechanical effects of 

 excitation we must further consider the variations in thickness of 

 the muscle and the propagation of excitation along its fibres. In 

 excitation the long axis of the muscle shortens, and its transverse 

 axis increases, while the surface of the muscle diminishes during 

 the contraction and increases in relaxation. But the question was 

 long disputed as to whether the volume of the muscle also varied 

 during contraction, and diminished during tetanus. This question 

 was experimentally investigated long since by Borelli, Glisson, 

 Swammerdam, and subsequently with better methods by Barzel- 

 lotti, Erman, Job. Mliller, E. Weber, and many others. The 



