{HEAD ~ The selective transmission} may be achieved by providing {TAIL ~ a wall section} consisting of a selectively permeable material, chosen to permit the transfer of only the gaseous substance to be monitored between the interior and the exterior of the chamber 
{ HEAD ~ The selective transmission } may be achieved by providing { TAIL ~ a wall section } consisting of a selectively permeable material , chosen to permit the transfer of only the gaseous substance to be monitored between the interior and the exterior of the chamber
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH