{HEAD ~ a second flow sensor} in {TAIL ~ fluid communication} with the second one of the reagent storage reservoirs 
{ HEAD ~ a second flow sensor } in { TAIL ~ fluid communication } with the second one of the reagent storage reservoirs
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH