GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 133 



continuous. If the surface of a muscle be exposed and be wet and glistening, 

 the light reflected from it during continued contractions is seen to flicker, as 

 if the surface were shaken by fine oscillations. In fatigue the muscle passes 

 from apparently continuous contraction to one exhibiting tremors, and mus- 

 cular tremors are observed under a variety of pathological conditions. 



With these facts in mind, a number of observers have endeavored to dis- 

 cover the rate at which the muscle is normally stimulated. Experiments in 

 which muscles have been excited to incomplete tetanic contractions by induced 

 currents, interrupted at different rates, have shown that the muscle follows the 

 rate of excitation with a corresponding number of vibrations, and does not 

 show a rate of vibration peculiar to itself. Further, it has been ascertained 

 that the sound given out by a muscle excited to complete tetanus, i. e. an 

 apparently continuous contraction, corresponds to the rate at which it is ex- 

 cited. Apparently, any rate of oscillations detected in a muscle during normal 

 physiological excitation would be an indication of the rate of discharge of 

 impulses from the central nerve-cells. 



Wollaston was the first to observe that a muscle gives a low dull sound 

 when it is voluntarily contracted, and that this sound corresponds to a rate of 

 vibration of 36 to 40 per second. It may be heard with a stethoscope placed 

 over the contracting biceps muscle, for instance, or if, when all is still and the 

 ears are stopped, one vigorously contracts his masseter muscles. Helmholtz 

 placed vibrating reeds consisting of little strips of paper, etc., on the muscle, 

 and found that only those which had a rate of vibration of 18 to 20 per 

 second were thrown into oscillation when the muscle was voluntarily contracted. 

 This observation indicated that the muscle had a rate of vibration of 18 to 20 

 per second, a rate too slow to be recognized as a tone. He concluded that the 

 tone heard from the voluntarily contracted muscle was the overtone, instead 

 of the true muscle-tone. The consideration that the resonance tone of the 

 ear itself corresponds to 36 to 40 vibrations per second, makes it question- 

 able whether the muscle-sound should be accepted as evidence of the rate of 

 normal physiological excitation ; nervetheless, the experiments with the 

 vibrating reeds remain to indicate 18 to 20 per second to be the normal 

 rate. 



Within the last few years a number of researches bearing upon this question 

 have been published, and the results of these point to a still slower rate of vol- 

 untary excitation, varying from 8 to 12 per second according to the muscle on 

 which the experiment is made. Loven 1 discovered in the tetanus excited in 

 frogs poisoned with strychnia, and in voluntary contractions, both by mechani- 

 cal methods and by recording the electrical changes occurring during action 

 with the capillary electrometer, rates of 7 to 9 per second. Horsley and 

 Schafer 2 excited the brain cortex and motor tracts in the corona radiata and the 

 spinal cord of mammals by induct ion shocks, at widely differing rates, and 

 recorded the resulting muscular contractions by tambours placed over the 

 muscles. They observed oscillations in the myograms obtained which had a 



1 Cenlralblatt for die medicinischen fVissenschaften, 1881. 



2 Journal of Physiology, 1886, vii. p. 96. 



