Per the title, John Brown's Body is an epic American poem written by Stephen Vincent Benet. Its title references the radical abolitionist John Brown, who raided Harper's Ferry in West Virginia in the fall of 1859.
This episode takes place from March 1955 to March 1956.
The only episode of the series where, during the Alfred Hitchcock last appearance, after the show, there are two shots: one of him and another showing something else. In this case, a close up on his hands.