Electrical Characteristics of Living Systems *

Ever since the picturesque description of "animal electricity" by Galvani in the latter part of the eighteenth century, it has been tacitly assumed that electrical phenomena could be found associated with many biological processes. In fact, in recent years, a score or more of distinguished investigators have been studying the alternating current characteristics of the nervous system. These studies have been primarily concerned with the similarities of the action current in nerve fibers and of alternating wave phenomena in electricity. The development of instruments for studying these phenomena has been largely patterned after commercial designs. With the help of great magnification and refined methods of recording, the minute changes in electrical potential in nerve fibers during the passage of an action current have been studied. The results to be obtained by such investigations, in all probability, must be limited, since they record only the action current and not the characteristics of the fiber transmitting the action current. The very nature of the instruments used bars them from recording with any real accuracy potential characteristics other than those of an alternating character and yet direct current elements must be present. Observations on these polar differences have not been made, frequently because up to the present all current-measuring devices require current for their operation. It is obvious that any sensitive instrument which draws current will impose changes of greater or less magnitude on the electrical characteristics of the thing measured. Moreover, the passage of an electrical current through a measured living system polarizes the interfacial membranes in that system. Thus a second artefact appears in such measurements. Ideally, the measurement of potential differences in a living system should be made by a voltmeter or other measuring device which draws no current, and with the aid of electrodes, which are non-polarizing.t With such an instrument, it would be possible