Whether the tiny electrical current from the laying on of hands, or from a machine, the theory is that the electro-chemical bond by which pathogens and parasites link to cells at a special docking site is scrambled. They float off and die without being able to take nutrients from healthy cells. This isn't blasting the pathogen or parasite to death, just preventing it from getting nourishment from the cell. Neat, huh? So there is no damage to healthy tissue.
The Clarke Zapper would clean up all these blood-borne pathogens and parasites. These can get into the bloodstream from Leaky Gut Syndrome, for example, when Giardia or Candida eats through the gut wall. The Beck Magnetic Pulser is an electromagnetic device which blasts into deep lymph tissue. Beck also used Silver Colloid internally as a specific for cleaning up intestinal bugs and for topical use. The pure silver hyperoxygenates pathogens and parasites to death in their one-celled stage. I would use a more parasite-specific protocol like ParaGONE for intestinal cleansing of mature parasites.
Hulda Clark e originally used her Zapper device on the hands, nice and close to the pulse points. Beck's Silver Pulser device is used for blood cleaning at pulse points. The Magnetic Pulser is used on lymph sites. Beck's devices are sold by: http://www.sotainstruments.com/ or Beck's plans are available on the net (SEE: posting on Beck). Beck's Pulser is used on one arm or leg, so there is no current arcing through the trunk which could scramble a Pacemaker, for example. Hope this helps!