PHYSICS

stun prey. The strong current is used almost exclusively as a
weapon to attack prey.
17.2. ELECTROTHERAPY
Electrotherapy is the treatment of medical disorders using
electrical methods - in particular, electrodes or instruments that
apply some sort of electrical field, current or impulses to the
body. There are several different electrotherapy techniques.
17.2.1. Methods of Electrotherapy
Iontophoresis is the ion transfer of topical solutions into the
epidermis and mucous membranes using continuous direct current
through electrodes applied to the body. This medical technology
can be used for treatment of edema, skin ulcers, pain,
inflammation, tendonis-bursitis-arthritis, fungus, calcium
deposits and scar tissue. Iontophoresis can also be used to study
neurotransmitters in the brain through the application of
experimental solutions to the tissue using fine glass electrodes.
Transcutaneous Electrical Nerve Stimulation (TENS) Therapy is a
method used for pain relief. In TENS therapy, electrodes are
placed on the skin, either directly over the painful area or more
commonly at key points along the nerve pathway. A small, battery-powered
generator emits a milliampere of electricity through
lead wires to the electrodes.
Galvanic current is a constant and direct current having opposite
poles - positive (anode) and negative (cathode). The positive
pole has an acidic reaction - soothes nerves, decreases blood
supply and hardens tissues. It may be used to make flabby skin
and tissues firmer, to close skin pores after a facial treatment, to
decrease redness as in mild acne, and to prevent inflammation.
The negative pole has an alkaline reaction - it irritates nerves,
increases blood supply and softens tissues. This pole may be used
to remove superfluous hair by electrolysis, to force bleaching solution
into skin and to stimulate the circulation and nutrition of
dry, pale skin and scalp.
Faradic current is an alternating and interrupted current capable
of producing a mechanical reaction without a chemical effect.
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When a faradic current is applied to the body, the muscles are
toned and the circulation of blood improved. It stimulates hair
growth and increases glandular activity. Faradic current may be
used during facial mani pulations, but it cannot be used for pain
or discomfort, high blood pressure, broken capillaries or a pustular
condition of the skin.
17.2.2. Physiological Effects of Electricity
Electricity has at least three major effects that may be undesirable
- electrolysis, heating and neuromuscular stimulation.
Electrolysis is the movement of ions in opposite directions
through a medium. Electrolysis takes place when a direct current is
passed through any medium which contains free ions. If two
electrodes are placed on the skin, and a direct current of 100 mA
is passed beneath them for a few minutes, small ulcers will be
formed beneath electrodes. These ulcers can be painful and take a
very long time to heal.
Thermal Heating. When an electric current passes through any
substance having resistance (R), heat is produced. The amount of
heat depends on the power dissipated (Q = PR). High-frequency
electric currents are responsible for heating. The local effect of
heating depends on the tissue, the length of time it is heated, the
contact area and the blood flow. Electrical burns often produce
their most marked effects near the skin. Burns have been
produced by a current density of only 5 rnA/mm 2 for 10 s.
Neuromuscular Stimulation is potentially the most dangerous
physiological effect of electricity, in that the nervous system controls
both the circulation of the blood and respiration. Because
the body is a good conductor of electricity and our nerves and
muscles function electrically, physiological effects occur when a
current is applied to the body. If a current of sufficient amplitude
is passed between a pair of surface electrodes, the muscles will
contract because a stimulus is being introduced to the nerve
fibers, which control the muscles. The prolonged involuntary contraction
of muscles caused by an external electrical stimulus is
called tetanus. Prolonged tetanus of the muscles between the ribs
(intercostal muscles) can prevent breathing; tetanus of the heart
musculature prevents blood being pumping out of the heart.
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