Menace from the Microcosm by John Russel Fearn

Science fiction novella, not about giant worlds in outer space, but about microworlds closer to us. "It seemed to me," wrote the author, "that the conception of intra-atomic worlds, though by no means novel, had not so far been explored in all its possibilities... It gave me great pleasure to debate the possibilities while I wrote it; I hope that some of you at least will have an equal pleasure in reading it."

John Russell Fearn (1908–1960) was a British author and one of the first British writers to appear in American pulp science fiction magazines. Always a highly prolific author, he published not only under his own name, but also as Vargo Statten and other pseudonyms including Thornton Ayre, Polton Cross, Geoffrey Armstrong, John Cotton, Dennis Clive, Ephriam Winiki, Astron Del Martia (and others). He remains best known for his long-running Golden Amazon saga. At times these drew on the pulp traditions of Edgar Rice Burroughs. Fearn also wrote Westerns and crime fiction.