The barrier may be either a fluid permeable matrix or a fluid gap with {HEAD ~ a thin, fluid permeable membrane} for blocking {TAIL ~ convection currents} but otherwise admitting fluid and analyte 
for blocking
The barrier may be either a fluid permeable matrix or a fluid gap with { HEAD ~ a thin , fluid permeable membrane } for blocking { TAIL ~ convection currents } but otherwise admitting fluid and analyte
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH