{HEAD ~ The reagent composition} contains {TAIL ~ complement} and cells which contain quantitatively determinable substance therein 
contains
{ HEAD ~ The reagent composition } contains { TAIL ~ complement } and cells which contain quantitatively determinable substance therein
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH