He Who Shrank is a science fiction novella by Henry Hasse, printed as the featured story in the August 1936 issue of Amazing Stories magazine (illustrated on the cover and in its interior pages by Leo Morey). It is about a man who is forever shrinking through worlds nested within a universe with apparently endless levels of scale. It was reprinted in the 1946 collection Adventures in Time and Space, edited by Raymond J. Healy and J. Francis McComas, and in Isaac Asimov's anthology of 1930s science fiction Before the Golden Age. Plot A world-celebrated professor reveals to his assistant, the tale's narrator, that he has discovered that the visible universe at the largest scales corresponds to the microscopic universe at the smallest observed scales, the relations between the universe's planets, suns, and star clusters being identical to the relations of electrons, atomic nuclei, and molecules. Rather than explore the universe at their own scale, the professor intends to explore the worlds endlessly nested within matter itself which, he argues by induction, must go on to ever smaller levels, and claims to have invented a substance that, once applied, will cause an individual to perpetually shrink. His assistant thinks he's insane, but the professor, surprising the assistant, injects him with the substance, temporarily paralyzing the assistant and dooming him to eternally shrink ever smaller, through successively smaller worlds, each a subatomic particle of the previous one (the injected substance, "Shrinx", has engineered secondary properties, such as oxygenating the blood and protecting against heat loss in space). The professor will monitor the assistant's fate through a device that receives his sense of sight and sound, and intends to eventually follow suit and set himself shrinking as well, although they would never meet again due to the infinitesimal chance of tracing the same path through the subatomic worlds. The assistant, sent as an involuntary scout, shrinks further and further, through the peril of being attacked by a microorganism, down to various worlds, inhabited by various beings who, at their time scales, have seen him approach for years or centuries, including intelligent gaseous beings, cave people, space-faring birdlike beings who flee to their moon to escape self-replicating machines who have overrun their planet and will likely go on spreading through the universe at that scale, and others the narrator mentions only in passing, of widely varying forms. One race of intangible beings teaches