About 4.4 million hadronic decays of Z bosons, recorded by the OPAL detecto
r at LEP at a centre-of-mass energy of around roots = 91.2 GeV, are used to
determine the mean charged particle multiplicities for the three light qua
rk flavours. Events from primary u, d, and s quarks are tagged by selecting
characteristic particles which carry a large fraction of the beam energy.
The charged particle multiplicities are measured in the hemispheres opposit
e to these particles. An unfolding procedure is applied to obtain these mul
tiplicities for each primary light quark flavour. This yields
[n(u)] = 17.77 +/- 0.51(-1.20)(+0.86), [n(d)] = 21.44 +/- 0.63(-1.17)(+1.46
), [n(s)] = 20.02 +/- 0.13(-0.37)(+0.39),
where statistical and systematic errors are given. The results for [n(u)] a
nd [n(d)] are almost fully statistically anti-correlated. Within the errors
the result is consistent with the flavour independence of the strong inter
action for the particle multiplicities in events from the light up, down, a
nd strange quarks.