Dominus Vobiscum: Notes from a massgoer's underground
. . . where permitted but some prefer on tongue, then what?
Of course, says Congreg. of Divine Worship in February.
Moreover,
. . . let all remember that the time-honored tradition is to receive the host on the tongue. The celebrant priest, if there is a present danger of sacrilege, should not give the faithful communion in the hand, and he should make them aware of the reason for way of proceeding. [Emphasis added]
Note the concern. Note also that this is the Vatican before Francis.