Mortals are immortals, and immortals are mortals, the one living the other’s death and dying the other’s life.
 Bertrand Russell, A History of Western Philosophy (1945). copy citation

Context

“Heraclitus, though an Ionian, was not in the scientific tradition of the Milesians.* He was a mystic, but of a peculiar kind. He regarded fire as the fundamental substance; everything, like flame in a fire, is born by the death of something else. Mortals are immortals, and immortals are mortals, the one living the other’s death and dying the other’s life. “ All things come out of the one, and the one out of all things ” ; but the many have less reality than the one, which is God.
From what survives of his writings he does not appear as an amiable character.” source