THE PHENOMENON OF CONTRACTION. 



47 



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 

 muscles of the arms or fingers the series of electrical variations fol- 

 lows at the rate of 47 to 50 per second. Increase in strength of con- 

 traction in these muscles causes no change in rate, although a cor- 

 responding variation in the intensity of the electrical changes is 

 observed. When different muscles are studied by this method, 

 quite a marked difference in rate is obtained. Piper reports such 

 observations as the following: M. deltoideus, 58 to 62; M. gas- 

 trocnemius and M. tibialis anterior, 42 to 44; M. quadriceps 

 femoris, 38 to 41; M. massefer, 88 to 100, and M. temporalis, 80 

 to 86. Assuming that these figures represent the, rate of dis- 

 charge of nerve impulses per second by the nerve cells from 





Fig. 22. The upper curve shows the vibrations of the "string" of the string 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 par 

 second. (From Piper.) 



which arise the motor fibers to the muscles named, it is evident 

 that the various spinal and cranial motor centers may possess 

 quite widely different rhythms, although for each particular 

 center the rate is more or less fixed. Among the motor centers 

 thus far studied it will be noted that the cells of the N. trigeminus 

 possess the highest rate of discharge. There has been much 

 discussion as to whether or not we can obtain simple as well as 

 compound contractions by voluntary stimulation of our muscles. 

 It has been pointed out that in very rapid contractions, such as 

 occur in the trilling movements of the fingers in playing the 

 piano, the duration of the separate contractions is so brief as to 

 suggest that they may be of the order of simple contractions. 

 Direct investigation of such movements by the older method 



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

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

 345. 



