At pagan grammar school, St. Fidgeta's teacher Putricordes would frequently quote from this author's now lost attack on Christianity. A wax tablet (preserved in the convent of the Fidgettines in Fobbio) bears her [St. Fidgeta's] name and 'JMJ' at the top, and has farther down the page a note, which is labeled with the phrase "Jocus Prophyris" [St. Fidgeta & Other Parodies, 11].
Porphyry is, among other things, the name of Greek scholar and neoplatonic philosopher who wrote extensively against Christianity. It is also an igneous rock consisting of feldspar crystals embedded in a compact dark red or purple groundmass.
Porphyria is also the a group of inherited disorders that involves abnormalities in the production of pigments in the base material responsible for hemoglobin (red blood cell pigment) and myoglobin (reddish muscle cell pigment). The disorder is characterized by light sensitivity causing rashes), neuropsychiatric complaints, and complaints of pain or cramping. It is thought that King George III of Great Britain (1738-1820) suffered from this hereditary disease. Porphyria's Lover is a poem written 1834 by Robert Browning (1812-1889) about a madman in attempting to murder his lover by strangling her with her own hair.
Jocus (iocus) is Latin for joke; hence "joke of Prophyris."
In short, John was probably calling upon on his personal encyclopedia of odd facts for this one, says Bowen.
JMJ stands for "Jesus, Mary and Joseph," something we're told parochial school students perennially headed their homework and exam papers with, a pius invocation of the Holy Family.
