334 MOTION IN ANIMALS AND PLANTS. 



which constitute muscular action before us, it will ])e our purpose to 

 compare with this order that of its concomitant electrical phenomena. 

 Before I proceed with this comparison it is desirable to say that it 

 should be understood that no reference will be made to electrical 

 theory. We merely derive our modes of observation and of measure- 

 ment from the exact sciences and aimVt the utmost attainable pre- 

 cision; but the phenomena have their chief interest as outward and 

 visible signs of intimate vital processes, of which they afford us the 

 only knowledge that is within our reach. 



We choose as our subject of observation a muscle of nearly sjm- 

 metrical form — a band of parallel fibers. We explore its electrical 

 state by a conducting arch containing a galvanoscope, the ends of the 

 arch being in contact with its surface. If the muscle is no longer 

 living, the galvanoscope gives no evidence of current. If it is living, 

 there is again no current, provided that the two surfaces are in the 

 same ph3^siological state. If one is less living than the other, the fact 

 is indicated by a difference of potential between them, a current flow- 

 ing through the galvanoscope from the more living to the less living. 

 Vitality is, therefore, here indicated by difference of potential. By 

 vitality we mean nothing more than the capacity for discharging func- 

 tion. This capacity diminishes by discharge, i. e., by activity. Accord- 

 ingly \ve find that when, for an}^ reason, the muscular substance at 

 one part becomes more active than the muscular substance at another 

 the former becomes negative to the latter. 



Every observation of the electrical phenomena of muscle (or of any 

 other excitable structure) relates either to the state of capacity for 

 action (called in physiology "rest") or to the state of action or dis- 

 charge. In either case it consists in comparing the states of two con- 

 tacts,^ i. e., of two parts to which electrodes of a galvanoscope are 

 applied. It is obviously desirable for the investigation of the changes 

 at either that those which take place at the other should be annulled 

 during the period of observation. On this consideration a rule is 

 based, to the mode of carrying out of which I will advert presently. 



Most of the results which I shall place before you were obtained 

 with the aid of the capillary electrometer, of the use of which as an 

 aid to electrophysiological investigations I brought before the Royal 

 Society some instances nearly twenty years ago. Its application has 

 since been studied with great completeness by Mr. Burch, to whose 

 skill I am indebted for the instruments which I have used for my work 

 during the last ten years, and more particularly for the one which has 

 enabled me to submit to you the photographic results I am now about 

 to exhibit. These photographs, I need scarcely explain, express the 



^ It may be well to note that the contacts referred to here and elsewhere are made 

 by means of nonpclarizable electrodes of the kind originally devised bv Du Bois- 

 Reymond and always used in physiological work. 



