between these two stimulating factors-increased injury and increased nerve-until in 1958 when
Zhirmunskii reported that the current of injury was directly related to the extent of innervation (37).
This observation, coupled with the much earlier work of Matteucci that indicated a direct relationship
between the magnitude of the current of injury and the extent of the injury itself, suggested that the
current of injury was the factor common to both Rose's and Singer's experiments.
On this theoretical basis we measured the current of injury following foreleg amputations in
salamanders compared to the same amputation in frogs (38). While the immediate postamputation
potentials were positive in polarity and about the same in magnitude in both species, the frog's potential
slowly returned to the original slightly negative potential as simple healing by scarification and
epithelialization took place. In the salamander, the positive potential very quickly (3 days) returned to
the original base line but then became increasingly negative in polarity, coinciding with blastema
formation and declining thereafter as regeneration occurred. These observations regarding polarity and
duration of the potentials have recently been confirmed by Neufeld using the same techniques (39).
Fig. 2.6. Measurements of the current of injury following forelimb amputation in the frog (not capable
of regeneration) and in the salamander (capable of regeneration). The immediate effect is a shift to a
highly positive polarity in both animals. The frog slowly decreases this polarity as healing by
scarification occurs, while the salamander reverses the polarity, shifting negatively at about the third
day. Following this the blastema appears and regeneration occurs over a 3-week period, during which
the negative polarity slowly subsides.
As reviewed in the first chapter, the clinical use of externally generated electrical currents to
enhance healing or retard tumor growth was common in the latter half of the nineteenth century. While
the technique rapidly fell into disfavor in the early decades of the present century with the mounting
evidence against electrical properties of living things, some laboratory studies were continued. Frazee,
for example, studied the effect of passing electrical current through the water in which salamanders
were kept. In 1909 he reported that this appeared to increase the rate of limb regeneration in these
animals (27). In their long series of investigations extending from the 20's through the 40's, both Burr
and Lund reported growth effects of applied electrical currents on a variety of plants and animals.
Some of their observations were confirmed and extended by Barth at Columbia University (28).
Two observations were immediately pertinent to Bernstein's original theorization that the
current of injury was simply an expression of the transmembrane potential of damaged cells. The first
was the polarity reversal in the salamander at 3 days and the second was the persistence of the
potentials for several weeks until the injury was either healed closed or regenerated. Neither
ELECTROMAGNETISM & LIFE - 33