  We calculate the Casimir force between two parallel ideal metal plates when
there is an intervening chiral medium present. Making use of methods of quantum
statistical mechanics we show how the force can be found in a simple and
compact way. The expression for the force is in agreement with that obtained
recently by Q.-D. Jiang and F. Wilczek [Phys. Rev. B {\bf 99}, 125403 (2019)],
in their case with the use of Green function methods.
