Electricity, magnetism and the body: some uses and abuses.

The human body can be regarded as an extraordinarily complex electrical machine. It will respond to externally applied electromagnetic stimuli and aspects of its functionality can be interrogated electromagnetically to aid in diagnosis. The paper describes examples of interactions between electromagnetism and the body. The hazards of electric shock are considered along with the use of the defibrillator for restarting the heart. Electromagnetic therapies are discussed in the light of the disappointing lack of objective evidence to support claims for their effectiveness. Finally, two examples of new diagnostic techniques using electromagnetic energy are described. Electrical impedance tomography produces cross-sectional images of the distribution of electrical impedance in the body and magnetic nerve stimulation uses currents induced by large magnetic field pulses to stimulate nerves and the human brain without causing pain.