rat race

[Benjamin Fortson]

Hi everyone,
        I got a query from someone about "rat race". I had never really
thought about it, but is the image originally that of swarms of rats, or
of rats in a maze, or of something else entirely? Also, does anyone know
when it became "fixed" in the meaning of the struggle to get ahead? The
first OED cite (1939) is a bit ambiguous, and the second (1940) seems to
refer to a swarm of people; same goes I think for the next cite, from
1946. All that would seem to indicate that swarming was the operative
metaphoric spring-board, but the 1939 cite doesn't quite match that
("Their own private life gets to be a rat-race"). A 1947 cite is the first
one that seems clearly to refer to struggle and competition, and that
sense holds forever thereafter.
        Thanks!
Ben