Introduction
Safe and inexpensive diagnosis by skin level measurements may be superior to present imaging techniques which give limited information. An instrument is needed that can be expected to do this reliably and effectively (1), a role that is filled by the EDSD. Its acceptance will not come easily and requires adequate research evidence.

The EDST, is a testing process in which measurements are taken with the EDSD. Together they form the EDSS, a general term that stands for all the components. The device, the test procedure and the system are integrally related and cannot be separated. They must be understood together.

The EDSS is theoretically based upon bioenergy (chi) and traditional meridians which represent the paths of flow of this energy. The obvious way to prove that such energy exists is by using a device which measures it. This is what the EDSD can do. This article reviews the history, methodology and the current state of modern research in this field of investigation.

History
Biological energy, known as "chi" in traditional Chinese medicine, is generated in internal organs and flows through channels near the skin surface, known as meridians. Acupuncture points, generally located on meridians, are where the flow of the energy can be manipulated. The stimulation at these points by various means affects the energy circulation, thus producing secondary effects in connected organs and systems (2).

The use of the word "systems" as used hereon refers to the source areas of bio-energy in body organs and systems. It is not to be confused with the "meridian system" which refers to the complete network of meridians. A meridian, which includes the structure of the system of origin, the function of that system, the electromagnetic pathway and its emotional-vibrational interaction, can be conceived individually or as part of an intricate network. The synergistic totality of the meridian system is fundamental.

Although various mechanisms to explain acupuncture are offered, the electromagnetic model fits best. Analogically the systems can be compared with energy fields connected by wiring. A small "dose" of electromagnetic energy introduced through an acupuncture point flows to the connected system and affects it. Anything that alters system function or structure changes the energy flow through the "wiring" and the EDSD measures the resistance and polarization at the affected acupuncture points. It thus provides a picture of the balance of related systems that are interconnected through the "wiring."

Voll (3) was an early investigator who applied low voltage currents to acupuncture points in humans. His device was called the Diatherapuncteur, but the Dermatron (Pitterling Electronics, Munich) has replaced it. Voll's original goal was therapeutic electroacupuncture but he noted that the low voltage emitted by his device caused a response at the acupuncture point which reflected the condition of the associated system. Thus, it could be used in diagnosis and monitoring of a patient's health status and became known as electroacupuncture according to Voll (EAV). This was the revolutionary aspect of EAV which has led to development of EDST.