means for producing an electrical signal in the photodetector having a frequency component proportional to the blood cell velocity in {HEAD ~ response} to autodyne beating of Doppler shifted and {TAIL ~ non Doppler shifted radiation signals} 
means for producing an electrical signal in the photodetector having a frequency component proportional to the blood cell velocity in { HEAD ~ response } to autodyne beating of Doppler shifted and { TAIL ~ non Doppler shifted radiation signals }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL