Can I recover earlier version of Powerpoint presentation? I accidentally deleted the content and then (DOH!) saved it.

EIGHT hours into a Powerpoint presentation. Wanted to delete the content of a particular slide. Did a "command +A" (select all), hit delete...and then like a complete idiot, saved it, thereby overwriting all of the content. The file itself has not been deleted...now it's just a blank presentation with all content MIA. Previous to this screw up, there were 49 versions. Is there a way I can find the last version before my DEFCON LEVEL: BLONDE moment???