The first radioactive mutant ever?

I was reading a reprint of Action Comics #39 (August 1941) and, lo and behold, the story involves a guy mutated into an invulnerable killing machine by nuclear radiation.

Now after World War II, comic book characters mutated by radiation were common as dirt. A lot of the B-movies of the 1950s also used this idea. It was an incredibly convenient plot device--a quick way to explain how Godzilla was awakened after a multi-million year slumber; or why there are giant ants rampaging through the desert; or why Peter Parker suddenly has the proportional strength of a spider.

But before the war, when the average person was only vaguely aware of what radiation is, it didn't pop up as much. So it was interesting to run into the concept in a pre-war story.

So I've been wracking my brain trying to think of an earlier story in any medium that used the radioactive mutant conceit. I can only think of one that kinda, sorta qualified. A pulp magazine hero called the Green Lama first appeared in 1940. One of his tricks was drinking a solution of radioactive salt. This temporarily gave him the power to shock bad guys unconscious simply by touching them.

But that really isn't the same thing as a mutation into something monsterous or superpowered. Was this Superman story the first time this happened? I just don't know for sure. There might be a B-movie or something from Astounding Stories magazine that covered this ground first. Or there might not. It's one of those questions that there's really no effective way to research.

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But whether it was a first or not, the Superman yarn (recently reprinted in The Superman Chronicles, volume 6) is a pretty good one. With a good script by Jerry Siegel and good art by Leo Novak, it makes for an effective and slightly creepy horror story.