Contraction of Muscle During Innervation. 127 



The action currents were registered photographically as excur- 

 sions of the quartz "string "of a large Einthoven galvanometer, 

 and the results are in consonance with those of Piper, who found 

 the rate to be 47 to 50 variations per second. 



The muscle sound was made to register itself as electrical 

 variations by use in connection with the galvanometer of a very 

 delicate microphone, carefully protected against external vibrations 

 and connected with a stethoscope placed over the contracting 

 muscles. 



The rate of the sound as so determined is from 46 to 52 per 

 second, which agrees fairly well with the rate obtained by the pre- 

 ceding method. 



Unless great care is exercised to allow free ingress and egress 

 of air to and from the stethoscope, large waves of frequency, 10 to 

 13 per second, complicate the sound record. 



The mechanical movements were registered in the usual 

 manner with receiving and recording tambours and also with a 

 small telephone applied to the flexor surface of the forearm and 

 connected with the galvanometer. This is an extremely delicate 

 method of registering mechanical movements. 



The frequency obtained over contracting muscles was about 1 2 

 per second with both methods. 



Using the telephone method, curves of similar character and 

 frequency were obtained over the surface of the resting arm during 

 electrical stimulation of the flexor group of the other arm, and also 

 for a short time following such stimulation. 



These movements were also readily evoked in the resting arm 

 during voluntary contraction of the flexors of the opposite arm. 



The records of the action current do not show variations of the 

 slow rate when the galvanometer is so adjusted as to give an 

 optimum record of the 47 to 50 rate, but slow variations appear 

 on increasing its sensitiveness. 



It appears as a result of this study, that in voluntarily con- 

 tracting muscle there are two distinct sets of rhythmic phenomena. 

 One, occurring at the rate of 47 to 50 per second and due to vol- 

 untary impulses from the central nervous system ; the other, reflex 

 and occurring at a rate of from 10 to 13 per second. It appears 

 extremely probable that the latter are variations in tonus. 



