The action currents produced by heart muscle and other tissues immersed in or in contact with a large body of conducting material are distributed in accordance with the laws that govern the flow of electric currents in volume conductors.
The curve obtained when one electrode (the exploring electrode) is placed very close to and the other (the indifferent electrode) very far from the active tissue may be regarded as representing the potential variations of the exploring electrode alone; the. potential of the indifferent electrode is by comparison nearly constant.
Curves obtained by this method of leading from the surface of the mammalian auricle indicate that the electrical effects produced by the passage of the excitation wave along a single muscle fiber are nearly the same as those that would occur if the crest of this wave were immediately preceded by a source and followed by a sink.
A study of the electric field of a polarized membrane immersed in a volume conductor shows that this conclusion may be derived on theoretical grounds from the membrane theory of Bernstein.