A laser beam is focussed on to a capillary by means of a lens, mirror and beam splitter system and measurement of the velocity of the blood cells in {HEAD ~ a direction} substantially perpendicular to {TAIL ~ the surface} of the tissue is effected by detecting directly back scattered radiation 
substantially perpendicular to
A laser beam is focussed on to a capillary by means of a lens , mirror and beam splitter system and measurement of the velocity of the blood cells in { HEAD ~ a direction } substantially perpendicular to { TAIL ~ the surface } of the tissue is effected by detecting directly back scattered radiation
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