outlet conductivity cell 52 crosses the fourth tubing branch 70 of the inlet conductivity cell 54 at an angle approximately sixty degrees in the preferred embodiment at a sensing location an excitation coil 72 encircles the first tubing branch 60 of the outlet conductivity cell 52 and the third tubing branch 68 of the inlet conductivity cell 54 at the excitation location a sensing coil 74 encircles the second tubing branch 62 of the outlet conductivity cell 52 and the fourth tubing branch 70 of the inlet conductivity cell 54 at the sensing location an electrical circuit as is illustrated schematically in fig3 is thus formed the excitation coil 72 is inductively coupled to the outlet conductivity cell 52 and the inlet conductivity cell 54 when a source of excitation energy 76 causes an alternating excitation current illustrated by direction arrow 78 to flow in the excitation coil 72 a changing magnetic field is generated which causes an electrical current illustrated by the direction arrow 80 to flow in the blood in the outlet conductivity cell 52 and causes another electrical current illustrated by direction arrow 82 to flow in the same electrical direction in the blood in the inlet conductivity cell 54 since the conductivity cells 52 and 54 are formed to create electrical paths of equal cross sectional area and equal path length the electrical conductance of the paths as illustrated by the schematic resistors 84 and 86 and thus the magnitude of the induced currents 80 and 82 will be related to the conductivity of the blood in the respective conductivity cells 52 and.