CREATE TABLE table_74388 ("No. in series" FLOAT, "No. in season" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original air date" TEXT, "Production code" FLOAT)

What is the original air date of the episode with production code is 319?
SELECT "Original air date" FROM table_74388 WHERE "Production code" = '319'
SELECT "Original air date" FROM "table_74388" WHERE "Production code" = '319'