THE MUSCLE SOUND. 495 



pletely after fatigue, while, at the same time, there is a new increase in the produc- 

 tion of heat {Meade Smith). 



The amount of work and heat in a muscle must always correspond to the transformation of 

 an equivalent amount of chemical energy. A greater part of this energy is manifested as work, 

 the greater the resistance that is offered to the muscular contraction. When the resistance is 

 great, \ of the chemical energy may be manifested as work, but when it is small, only a small 

 part of it is so converted. 



It was stated that a nerve in action is ^V C. warmer (Valentin), but this is denied by 

 v. Helmholtz and Heidenhain. 



In man, if the muscles be stimulated with electricity or contracted voluntarily, the produc- 

 tion of heat may be detected through the skin (v. Ziemssen). The venous blood, flowing from 

 an actively contracting muscle is 0"6 C. warmer than the arterial blood (Meade Smith). 



303. THE MUSCLE SOUND. Muscle Sound. When a muscle contracts, 

 and is at the same time kept in a state of tension by the application of sufficient 

 resistance, it emits a distinct sound or tone with a semi-musical quality, depend- 

 ing upon the intermittent variations of tension occurring within it ( Wollaston). 



Methods. The muscle sound may be heard by placing the ear over the tetanically contracted 

 and tense biceps of another person ; or we may insert the tips of our index fingers into our ears, 

 and forcibly contract the muscles of our arm ; or the sound of the muscles that close the jaw 

 may be heard by forcibly contracting them, especially at night when all is still, and when the 

 outer ears are closed. V. Helmholtz found that this tone coincides with the resonance tone of 

 the ear, and he thought that the vibrations of the muscles caused this resonance tone. The 

 sound of an isolated frog's muscle may be heard by placing one end of a rod in the ear, the other 

 ear being closed. To the other end of the rod is attached a loaded frog's muscle kept in a tetanic 

 condition. The pitch of the note, i.e., the number of vibrations, may be estimated by com- 

 paring the muscle sound with that produced by elastic springs vibrating at a known rate. 



When a muscle contracts voluntarily, i.e., through the will, it makes 19 '5 vibra- 

 tions per second. [Schafer and others give the number as 10 successive nervous 

 impulses per second, p. 486.] We do not hear this very low tone, owing to the number 

 of vibrations per second being too few, but what we actually hear is the first over- 

 tone, with double the number of vibrations. The muscle sound has 19*5 vibrations, 

 when the muscles of an animal are caused to contract, by stimulating its spinal cord 

 (v. Helmholtz), and also when the motor nerve-trunk is excited by chemical means 

 (Bernstein). If, however, tetanising induction shocks be applied to a muscle, then 

 the number of vibrations of the muscle sound corresponds exactly with the number 

 of vibrations of the vibrating spring or hammer of the induction apparatus. Thus, 

 the tone may be raised or lowered by altering the tension of the spring. 



Loven found that the muscle sound was loudest, when the weakest currents capable of pro- 

 ducing tetanus were employed. The sound corresponded to the number of vibrations of the 

 octave just below it in the scale. With stronger currents the muscle-sound disappears, but it 

 reappears with the same number of vibrations as that of the interrupter of the induction ap- 

 paratus, if still stronger currents are used. 



If the induction shocks be applied to the nerve, the sound is not so loud, but it 

 has the same number of vibrations as the interrupter. With rapid induction 

 shocks, tones caused by 704 (Loven) and 1000 vibrations per second have been 

 produced (Bernstein). 



The first heart-sound is partly muscular ( 53). 



A single induction shock is said to cause the muscle-sound in a contracting muscle. If this 

 be so, it is doubtful if the muscle-sound can be regarded as a sign that tetanus is due to a 

 series of single variations of the muscle ( 298, III.). 



304. FATIGUE AND RECOVERY OF MUSCLE. Fatigue. By the term 

 fatigue is meant that condition of diminished capacity for work which is produced 

 in a muscle by prolonged activity. This condition is accompanied in the living 

 person with a peculiar feeling of lassitude, which is referred to the muscles. A 

 fatigued muscle rapidly recovers in a living animal, but an excised muscle recovers 

 only to a slight extent (Ed. Weber, Valentin). 



[Waller recognises a certain resemblance between experimental fatigue and the natural decline 

 of excitability at death, in disease, and in poisoning.] 



