



THE ELECTRICAL PROPERTIES OF MUSCLE. 407 



the body. The muscles work with relatively little expenditure of 

 thermogenetic material, because, for the most part, each effort is preceded 

 and prepared for by previous extension. 



Looking at this subject in a more general way, and seeing that even 

 curarised muscles have a certain power of regulating their own 

 expenditure in accordance with the work they are required to do, 

 the experimental data which we have had before us indicate that this 

 regulation is such as must unquestionably tend to the advantage of the 

 organism. 



THE ELECTRICAL PROPERTIES OF MUSCLE. 



In all excitable organs differences of potential present themselves 

 between different parts of the surface, which cannot be attributed to 

 accidental or external, physical or chemical conditions. These have 

 a definite relation to the structure of the organ, to its general state 

 of functional activity, and to the relative state of functional activity 

 of its parts ; so that when the whole organ or any part of it passes 

 from the state of rest (relative inactivity) to that of activity, or 

 the reverse, this change is indicated by a corresponding change in the 

 distribution of electrical tension (i.e. of differences of potential) at its 

 surface. These changes of tension can be investigated with the aid of 

 suitable instruments. They derive their importance from their correla- 

 tion with the physiological changes which they accompany. This 

 correlation can be determined by the comparison of concomitant 

 variations of different orders, i.e., of variations of functional activity 

 on the one hand, with variations of distribution of electrical tension 

 on the other. If the parts of the surface of an organ between which 

 differences of potential exist, are so connected with a galvanoscope 

 that they are included in its circuit, they are of course indicated in the 

 instrument as currents. As some form of galvanoscope is generally 

 used as the means of investigation, the variations or states so observed 

 are ordinarily spoken of as " currents." Those currents which indicate 

 the normal distribution of tension on the surface of muscle are called 

 currents of rest, or "muscle currents." Those which appear as con- 

 comitants of transition from relative rest to functional activity, are 

 called " action currents." With reference to all of them, it has to be 

 remembered that what is observed and measured is not what occurs 

 in the organ under investigation, but in the galvanoscope. For 

 although currents actually exist in the organ itself, we learn nothing 

 by our observation, either as to their direction or relative strength. All 

 that is revealed to us, when we compare the two parts of the surface by 

 applying to them the terminals of our galvanoscopic circuit, is the 

 measurable difference of potential between the two parts. 



Electromotive phenomena of muscle in the unexcited state. 

 Inasmuch as the electrical changes which accompany increase, diminu- 

 tion, or cessation of functional activity, can only be spoken of in their 

 relation to the normal state from which the structure has departed, 

 and to which it tends to return, it is obviously desirable that the study 

 of that state the state of relative rest should precede that of activity 

 or disturbance. 



It is important in the employment of muscles for the investigation 

 of electromotive phenomena, to distinguish between those which are 



