{HEAD ~ Gas} can be introduced into the liquid in any one or all of {TAIL ~ the chambers} 
{ HEAD ~ Gas } can be introduced into the liquid in any one or all of { TAIL ~ the chambers }
HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL