Experimental study of the migration of charcoal particles in the human mouth.

Suspensions of charcoal in water, placed in the vestibule on one side of the mouth, spread within about 5 min to the dorsum of the tongue and the hard palate on the same side but did not cross the mid-line. When placed centrally under the tongue, the movement of charcoal was equally rapid but it spread over the whole surface of the mouth.