treat of (something)
archaic To be concerned with or focused on some subject or topic. The essay treats of the moral and philosophical implications of several theoretical economic models. A brief history of the city was given by the mayor, treating of its establishment as a mining colony in 1887 and its eventual evolution as a major business center for the entire country.
treat of
v. To deal with some subject or topic in writing or speech: The essay treats of courtly love.