The Electi'ical Response of Muscle 233 



pi. i., figs. 1, 2, 3], preceding the response of the flexors to a single break 

 induction shock applied to the median nerve, it would appear that the tibre 

 then in use took about, or nearly, three times longer to regain its resting 

 position (i.e. 4 to 5cr) than did the meniscus of my electrometer, and, more- 

 over, that the greater the excursion caused by the shock the longer was the 

 time it took to regain it. 



A record which Dr Piper was kind enough to send me at my request, 

 of a series of very weak induction shocks of a 50 per second frequency, 

 led into the fibre of the galvanometer he was using in his first set of ex- 

 periments, showed that the fibre hardly halted (if it did so at all) at its 

 resting position while passing it in either direction. The only record 

 reproduced of the response of the flexors to artificial excitation of the 

 median nerve by induction shocks of this frequency [(1) pi. i., fig. 3] was 

 taken with the same fibre, and shows that it then never halted and that the 

 swings were all precisely identical. 



Knowing from Einthoven's work (9) how beautifully the string- 

 galvanometer can be adapted to record accuratel}- any kind of small 

 electrical changes, I do not for a moment doubt that a fibre of (i.) such 

 normal sensitiveness, (ii. ) of such length, (iii.) of such resistance in proportion 

 to that of the electrodes used and of the skin and the tissues lying between 

 the electrodes and the muscle, (iv.) of such tension that its excursion is 

 shorter than that, not only of some, but of all the variations it is likel}^ to 

 have to record, and yet (v.) so damped that it has no periodicity of its own 

 — that such a fibre could be chosen and placed in such a magnetic field that 

 it would reproduce the electrical variations which occur in human muscle in 

 voluntary contraction better than the capillary electrometer can ever hope 

 to do. Yet just because it has to be adapted to what it has to record, it 

 seems to me that the string-galvanometer can never take the lead in giving 

 information about electrical changes the strength of which and the frequency 

 of which are unknown. A fibre of such kind and so arranged (as Piper 

 says his was) as to reproduce accurately the electrocardiogram of man, is 

 by no means therefore fitted to reproduce accurately electrical varia- 

 tions, seldom of much greater amount and some of them of smaller amount, 

 recurring with a much greater frequency. It seems to me that it is not 

 until a quick capillary electrometer has shown the nature of the varia- 

 tions to be registered that the time has come for the string-galvanometer 

 to help us to understand better than we can from its own records what 

 these mean. That it can then do it better follows from the fact that it 

 records directly the relative diflerence of potential at each moment, 

 whei-eas capillary electrometer records have always first to be inter- 

 preted in order to show this ; and although it is easy enough for anyone 

 accustomed to dealing with them to roughly interpret them at a glance, 

 to do so accurately involves a great deal of time and labour. 



Until I know, therefore, that the special fibres used by Piper were so 

 chosen and so arranged that they had no periodicity of their own, and that 



