In almost all experiments, the basic signal-energy mechanism employed
has been essentially that one studied most extensively by Lillie (12),
Bonhoeffer (2), Yamagiwa (22), Matumoto and Goto (14) and others,
_i.e._, activation, impulse propagation and recovery on the normally
passive surface of a piece of iron immersed in nitric acid or of
cobalt in chromic acid (20). The iron we have used most frequently
is of about 99.99% purity, which gives performance more consistent
than but similar to that obtained using cleaned “coat-hanger” wires.
The acid used most frequently by us is about 53-55% aqueous solution
by weight, substantially more dilute than that predominantly used by
previous investigators. The most frequently reported concentration has
been 68-70%, a solution which is quite stable and, hence, much easier
to work with in open containers than the weaker solutions, results in
very fast waves but gives, at room temperatures, a very long refractory
period (typically, 15 minutes). A noble metal (such as silver, gold
or platinum) placed in contact with the surface of the iron has a
stabilizing effect (14) presumably through the action of local currents
and provides a simple and useful technique whereby, with dilution,
both stability and fast recovery (1 second) can be achieved in simple
demonstrations and experiments.
Experiments involving the growth by electrodeposition and study of
metallic dendrites are done with an eye toward electrical, physical
and chemical compatibility with the energy-producing system outlined
above. Best results to date (from the standpoints of stability,
non-reactivity, and morphological similarity to neurological
structures) have been obtained by dissolving various amounts of gold
chloride salt in 53-55% HNO₃.
An apparatus has been devised and assembled for the purpose of
containing and controlling our primary experiments. (See Figure 1).
Its two major components are a test chamber (on the left in Figure
1) and a fluid exchanger (on the right). In normal operation the
test chamber, which is very rigid and well sealed after placing the
experimental assembly inside, is completely filled with electrolyte
(or, initially, an inert fluid) to the exclusion of all air pockets and
bubbles. Thus encapsulated, it is possible to perform experiments which
would otherwise be impossible due to instability. The instability which
plagues such experiments is manifested in copious generation of bubbles
on and subsequent rapid disintegration of all “excitable” material
(_i.e._, iron). Preliminary experiments indicated that such “bubble
instability” could be suppressed by constraining the volume available
to expansion. In particular, response and recovery times can now be
decreased substantially and work can proceed with complex systems of
interest such as aggregates containing many small iron pellets.
The test chamber is provided with a heater (and thermostatic control)
which makes possible electrochemical impulse response and recovery
times comparable to those of the nervous system (1 to 10 msec). The
fluid-exchanger is so arranged that fluid in the test chamber can be
arbitrarily changed or renewed by exchange within a rigid, sealed,
completely liquid-filled (“isochoric”) loop. Thus, stability can
be maintained for long periods of time and over a wide variety of
investigative or operating conditions.
Most of the parts of this apparatus are made of stainless steel and
are sealed with polyethylene and teflon. There is a small quartz
observation window on the test chamber, two small lighting ports, a
pressure transducer, thermocouple, screw-and-piston pressure actuator
and umbilical connector for experimental electrical inputs and outputs.