Elwood Ralson, a brilliant but psychologically disturbed
physicist, becomes convinced that humanity is a kind of
genetics experiment being run by an
alien intelligence. His behaviour becomes more erratic and suicidal as his thoughts become more entrenched in this idea, and his health fails. He draws an analogy between human progress and the growth of
bacteria that suggests that humanity has been bred in certain strains for various traits (e.g. artistic ability) and that such breeding is what produced the Athens of
Pericles and the
Renaissance. He further states that the experimenters use a
penicillin ring, or killing boundary, that makes humans want to kill themselves should their abilities grow too great, as mental increase leads to greater "infectivity," and humanity is dangerous to the experimenters. The most recent strain began with the
Industrial Revolution, and its development for over a century has made it extremely dangerous. Therefore, the theoretical experimenters intend to use the
atomic bomb to incite industrialized nations to kill each other. He claims that the aliens are exerting pressure on his mind to kill himself before he can help produce a defence against atomic weapons, since such a defence would protect humanity against a planned extinction at the hands of the aliens. Under the care of
psychiatrist Dr. Blaustein, Ralson is able to safely provide piecemeal guidance to other scientists carrying out his research. Once the experiment is complete and the defence (a
force field generator) is built and successfully tested, he commits suicide. Later, the man who assembled the force field generator, who never spoke to Ralson and did not know about his beliefs, also kills himself. ==Reception==