The resistance to
flow, especially with short boluses, was at least ten times greater than that associated
with Poiseuille flow. In a second series of experiments at lower Reynolds
numbers, a single bolus of liquid was forced by air pressure along a glass tube.
In these latter experiments, which more closely simulate biological conditions,
the mean resistance to flow was only 30 per cent greater than that associated
with Poiseuille flow. In the final series of experiments human blood and plasma,
diluted in acid-citrate dextrose (A.C.D.) in varying degrees, were forced through glass micropipettes of capillary dimensions. The mean apparent viscosity
of whole blood was found to exceed that of plasma by only about 5 per
cent, thus verifying a conjecture to this effect made by Fahraeus and Lindqvist
in 1931.