c) detecting {TAIL ~ light} of such wavelength that is reflected or scattered by {HEAD ~ said test element}, and 
c ) detecting { TAIL ~ light } of such wavelength that is reflected or scattered by { HEAD ~ said test element } , and
OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH