One of a number of words found in Dracula. Except not in Dracula, in the foreword to the edition I read (a tie-in to the Francis Ford Coppola film).

per·fer·vid /pərˈfɜrvɪd/
very fervent; extremely ardent; impassioned: perfervid patriotism.
[Origin: 1855-60; < NL perfervidus. See per-, fervid]

Related forms
per·fer·vid·i·ty, per·fer·vid·ness, noun
per·fer·vid·ly, adverb
per·fer·vor; especially British, per·fer·vour, noun