Diathermy
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Diathermy is the use of electrical current in surgery as either a cutting tool or to cauterize blood vessels to stop bleeding.
To set up a patient in the operating theathre for diathermy, a conductive pad is first placed on the patient, away from the site of surgery. The other contact point is an instrument wielded by the surgeon. Both of these are linked to the diathermy machine which has various settings for intensity and waveform.
A lesser known fact about diathermy is why the current passing through the body does not induce ventricular fibrillation or other arrhythmias in the heart. The reason it does so is that the current used is an alternating current which has a very high frequency (usually above 50,000 Hz), which changes polarity so fast that ions across the cell membranes in the body do not have enough time to be pulled over from one side to the other before the polarity changes again, thereby avoiding inadvertent depolarization of the cells.
Another design feature of diathermy explains why it only causes heating at the diathermy end - because the instrument tip has a much smaller area (almost a point) than the other electrode pad on the patient, the current density passing through the body at that end is much higher and therefore heat generated there is much more concentrated and sufficient to burn.
The invention of diathermy has made the work of surgeons much simpler by allowing them save time on hemostasis by burning off small arteries that would previously have had to be tied manually.