{HEAD ~ at least one metallic electrode} extending through {TAIL ~ said passageway} and not contacting said casing, and 
extending through
{ HEAD ~ at least one metallic electrode } extending through { TAIL ~ said passageway } and not contacting said casing , and
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH