Marvel Family #44 (1950)

Professor Andrew Jansen's automated survey rocket returns to Earth with samples collected while on Mars. The most startling thing brought back is a kind of bacteria, which rusts anything it touches. This strange lifeform is what's responsible for all the rust-covered rock formations on Mars, and he's determined to keep them contained until something that can counteract them is found. However, Michael Gordon, his assistant, owes money to a crooked casino owner, Ace Marlowe. To get out of a beating for not paying back his debt, Gordon instead shows him the rust-creating bacteria and how it can be used to disable alarms and eat through vaults. The Marvels investigate the robbery, but Gordon pours a sample of the bacteria at their feet to make them fall into the basement so he and the other thieves can escape. The bacteria sinks into the ground and eats into a water main. Soon it's spread so much a building collapses on top of the kids. Everyone survives, but Billy suffers a throat injury and can't say his magic word. He manages to make it to the station and uses a sound effects device to cast ghostly voices to amplify his own voice, letting him transform. He tries multiple chemicals to counteract the bacteria, only succeeding when he gets to his last resort: burning it. He observes this is a hopeless situation because he can't possibly burn everything down just to stop the bacteria! Meanwhile, Mary and Freddy recover enough to transform. Just in time for the villains to announce their plans to hold the city for ransom, else they'll release the bacteria on a wide scale. The Marvels attack their plane, but the spores are still dropped, and are soon flying all over to keep people from dying as buildings collapse. The villains have a falling out, with Ace Marlowe declaring things have gone too far, while Gordon declares as a scientist he's above moral concerns. They scuffle and the last sample of the bacteria is smashed over Marlowe, and he's soon consumed into nothing but a pile of rust shavings! Since they spilled on Gordon as well, he suffers the same fate. With no other ideas, Captain Marvel flies to Mars, and finds plant life there that's untouched by the rust bacteria. He isolates a cure from that, and the Marvels dump it into a storm cloud that destroys the deadly bacteria.