  J. M. Sancho [Phys. Rev. E 84, 062102 (2011)] analyzed two stochastic
interpretations on a recent experiment [Phys. Rev. Lett. 104, 170602 (2010)] of
Brownian colloidal particles. The author asserted that the stochastic
interpretation "obtained by simply setting the acceleration equal to zero"
should not be taken and that the zero-mass limit interpretation of the
experimental data would not be physically correct. In this Comment we show that
Sancho's analysis is incomplete in that it pre-excludes zero mass limit and
hence his assertions are incorrect. Our reasoning will be both mathematical and
physical.
