46 



THE PHYSIOLOGY OF MUSCLE AND NERVE. 



ployed. The contractions of the muscle have been recorded by 

 means of levers or tambours, so as to give a curve which can be 

 analyzed; the vibrations of the muscle have been estimated on the 

 principle of sympathetic resonance, and the musical tone emitted 



by the muscle during contrac- 

 tion has been determined. 

 The estimates arrived at by 

 these several methods all indi- 

 cated a relatively slow rhythm 

 of stimulation approximating 

 a rate of 20 stimuli per second. 

 The whole subject has been 

 reinvestigated more recently 

 by employing the "string 

 ^ >[ f galvanometer" (see p. 99) to 

 record the number of electrical 

 variations occurring during a 

 voluntary contraction. Since 

 each separate stimulus to a 

 muscle causes a distinct elec- 

 trical variation, it is evident 



that if we can record the number of such variations per second we 

 shall have almost conclusive evidence as regards the number of 

 simple contractions which enter into the production of voluntary 



Fig. 21. Schema to show the innerva- 

 tion of the skeletal (voluntary) muscles: 1, 

 the intercentral (pyramidal) neuron; 2, the 

 spinal neuron; 3, the muscle. 



Fig. 22. The upper curve shows the vibrations of the "string" of the strinir gal- 

 vanometer during voluntary contraction of the flexor of the fingers. Each vibration is 

 due to an electrical oscillation in the muscle (action current). These oscillations occur at 

 the rate of 50 per second, as may be seen by reference to the lower curve, the breaks in which 

 indicate fifths of a second. This fact would indicate, therefore, that in the voluntary con- 

 traction we have a tetanus composed of single contractions following at the rate of 50 per 

 second (From Piper.) 



tetanus. The string galvanometer lends itself to this purpose better 

 than any form of electrometer yet devised, and Piper,* by the use 

 of this instrument, finds that in voluntary contractions of the flexor 



* Piper, Pfliiger's "Archiv f. d. ges Physiologic," 1907, 119, 301; "Zeit- 

 schrift f . Biologie," 1908, 50, 393, and 504; "Archiv fur Physiologie," 1914, 345. 



