  We present measurements of the time-dependent fluctuations in electrical
current in a voltage-biased tunnel junction. We were able to simultaneously
extract the first three moments of the tunnel current counting statistics.
Detailed comparison of the second and the third moment reveals that counting
statistics is accurately described by the Poissonian distribution expected for
spontaneous current fluctuations due to electron charge discreteness, realized
in tunneling transport at negligible coupling to environment.
