  In I-Shih Liu's paper \C{1}, the compatibility of anisotropy and material
frame indifference of a rigid heat conductor is investigated. For this purpose,
the deformation gradient is introduced into the domain of the constitutive
mapping. Because of the presupposed rigidity, the deformation gradient is here
represented by an orthogonal tensor. The statement, that the usual procedure --
not to introduce the deformation gradient into the state space of rigid heat
conductors -- causes isotropy because of the material frame indifference, is
misleading.
