578 THE MUSCLE-MURMUR. 



The statement made by some that a rise in temperature, amounting to about 

 3^ C., occurs also in a nerve in action is denied by others; but an increase in 

 temperature does occur in a nerve in process of degeneration. 



5. As the muscle is an elastic body, thermal phenomena will occur in 

 it as a result of purely physical influences, as in inanimate, elastic bodies, 

 such as India rubber. Thus, heat is set free on stretching living or dead 

 muscle; and, conversely, the temperature of the muscle falls on elastic 

 shortening. 



THE MUSCLE-MURMUR. 



If a contracted muscle be at the same time maintained in a state of 

 tension by the application of resistance to it, a sound or murmur will 

 be audible, arising from intermittent variations in tension within the 

 muscle. 



Method. For purposes of observation, auscultation is practised either by 

 means of the ear applied directly, or with the aid of a stethoscope, over a tetani- 

 cally contracted muscle in another person. Some individuals are able to appre- 

 ciate the murmurs of their own muscles of mastication on closing the external 

 auditory canals, and pressing the jaws forcibly together. 



If one external auditory canal be closed, and into the other there be inserted 

 a small rod from the end of which is suspended a tetanized, weighted frog's muscle, 

 the sound of this isolated muscle can be readily heard. 



If the contracting muscle is attached to an elastic spring, whose rate of vibra- 

 tion can be varied, and if the rate of vibration is determined that must be im- 

 parted to the spring in order that it shall be energetically set into vibration by 

 the sounding muscle, the rate of vibration of the muscle-sound can be readily deter- 

 mined for each case after a few trials. A writing-style may be fastened to the 

 tip of the vibrating spring, and record the vibrations upon a smoked surface. 



A muscle, thrown into contraction by the will, vibrates from 19.5 to 20 

 times a second. The deep tone corresponding to such a small number of vibra- 

 tions is, however, not audible, but the first overtone, corresponding to twice 

 this number, is heard. The sound has the same rate of vibration when the muscle 

 is contracted in animals, by stimulation of the spinal cord, and also when the 

 motor nerve of a muscle is irritated by chemical means. If, however, the motor 

 center in the cerebral cortex be stimulated, the contracting muscle will generate 

 a tone that is the higher the stronger the stimulus. 



If a tetanizing induced current be applied to the muscle (also in man), the 

 rate of vibration of the muscular sound corresponds exactly with the rate of 

 vibration of the spring-hammer in the induction-apparatus. The sound can, 

 therefore, be raised or lowered by changing the tension of the spring. 



Loven found that the muscle-sound is relatively the strongest when the 

 weakest current is employed that will induce tetanus. The sound will then have 

 the vibration-rate of the next lower octave. As the current is increased in strength, 

 the muscle-sound disappears, and with a strong current it reappears with the 

 same rate of vibration as that of the interrupter of the induction-apparatus. 



If the induction-shocks are sent through the nerve, the sound is not so loud, 

 but otherwise it is of the same vibratory duration. By means of rapid induction- 

 shocks sounds have been produced up to 704 and 1000 vibrations in a second. 



The first sound of the heart is in part a muscle-sound. 



Landois, in 1873, first reported the observation that the rumbling murmurs 

 emitted by many fish (Cottus, sea-scorpion) are due to the loud sounds generated 

 by the spasmodically contracted muscles of the shoulder-girdle, and still fur- 

 ther intensified by the resonance of their large oropharyngeal cavity sur- 

 rounded by a firm bony framework. He found at that time that even a single 

 induction-shock that excited the muscles was able to generate the muscle-sound. 

 Herroun, Yeo, and Mac William also noted a like condition in the contracting mus- 

 cles of man. It must, accordingly, be considered as doubtful whether the muscle- 

 sound can be regarded as evidence that tetanus is made up of a series of fluctua- 

 tions in the density of the muscle. According to Bernstein, the sound heard 

 during contraction occurs in the latent period. Hence, the cause of the 

 muscle-sound is not to be sought in a displacement of the mass of the muscle. 



