Figure 3. In vitro and in vivo calibrations of the fluorescent light detection system.

Fluorescent light intensity, I_f (arbitrary units 0–250), for a series of concentrations of sodium fluorescein in BSA-Ringer perfusates. In vitro measurements (•) were determined with varying concentrations of fluorescent solution in a haemocytometer (100 μm pathlength). In vivo measurements (○) were made from video recordings of perfusions of a single capillary with 4 different sodium fluorescein solutions and with a fifth solution in which there was no sodium fluorescein. The vessel was assumed to be circular in cross-section and estimates of I_f were made from a small area over the centre of the vessel, vessel diameter 28 μm.