The Electrical Response of Muscle 231 



V. Conclusions to be drawn from the Foregoing Exi^eriments. 

 Further Experiments which favour them. 



The conclusions that I have come to from my own experiments, com- 

 paring the records obtained with human muscles with those before referred 

 to as obtained under simpler experimental conditions in the frog, and 

 having regard in each case to the difference of character between the 

 electrical responses to artificial discontinuous stimulation, by means of 

 induction shocks at the rate of about 50 per second, and to a central 

 stimulus, are : — 



(i.) There is no certain indication that the central stimulus is dis- 

 continuous at all (unless interrupted by other stimuli), but if it be so, the 

 separate stimuli are likely to be each what v. Kries has called a Zeitreiz. 

 Whatever its nature it is certainly not a series of instantaneous stimuli 

 recurring with a frequency of 50 per second. 



(ii.) The rhythm which appears in electrometer records of human 

 skin-covered muscle in voluntary contraction is as purely muscular in 

 origin as is that proved by experiment to be so in the bared muscle 

 of the frog thrown reflexly, or in a variety of other ways, into per- 

 sistent contraction ; its frequency may vary in different muscles, and 

 in different kinds of fibre in the same muscle, between 50 and 200 per 

 second. 



Piper's records, which lead him to conclusions so diametrically opposed 

 to these, differ from mine chiefly in exhibiting one pai'ticularly dominant 

 rhythm, which he thinks is constant in frequency for each muscle, so that 

 when a muscle is artificially excited by stimuli of the frecjuency denoted by 

 this rhythm, he finds great resemblance where I find great contrast 

 when a comparison is made with the voluntary response. 



The first thing which, of course, suggests itself in trying to account for 

 the discrepancy is the difference of recording instrument, or rather of 

 the particular pattern of each instrument, that we have been respectively 

 employing. In order to judge of the suitabilit}^ of a particular instrument 

 for recording electrical changes of unknown, but of possibly high, frequency, 

 and of unknown, but of probably varying, strength, we must in the first 

 place assure ourselves of the quickness with which the recording part of the 

 instrument can come back to its position of rest after it has been disturbed, 

 and ascertain that this is independent of the amount by which it has been 

 disturbed. To show to what extent the particular capillary electrometer I 

 have been using is suitable for the purpose, I therefore reproduce here not a 

 comparison curve (Aichungscur ve) but what seems to me to be more to the 

 point, the photographic record obtained when a series of break and make 

 induction shocks of a frequency of about 50 per second are allowed to 

 escape into a dead muscle, which is connected with the two terminals of the 

 electrometer. In order to be able to measure the intervals between the 

 successive ett'ects, the photograph (fig. 7) was taken on a much more rapidly 



