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. masseter, 88 to 100, and M. temporalis, 80 

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

 charge of nerve impulses per second by the nerve cells from 



TiK ~- — Ihe upper cui-\e -how-- the m'> -tiitiK" of the ^frint; Kal- 



vanoinetei dti'-ing voluiitai\ contraction of tin il \ i > liimt-i'- Ijach \iLiation i-. 



due to an eleccrital c-ciUation in tlie nui>-cle (action cuiumi Fhc so O'-cillation-. occur at 

 the rate of 50 per feecond, a-^ mav be "-een b\ lefeience to the lower cur\e tlie break-, in which 

 inciicate fiftlii of a '.econd Ihis fact would indicate therefore, that in the \oluntai\ con- 

 traction we have a tetauus uonipuscd of single uoiitiactiOua following at the latc uf M per 

 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. There has been much dis- 

 cussion 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 

 of recording with levers (von Kries) or by the newer method of 



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

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

 345. 



