The Enterprise investigates the strange case concerning a series of planets whose inhabitants seem to be overcome by mass insanity. A nearby ship flies straight into the sun, despite everything the Enterprise crew does to help it. After a few more peculiar communications, the trail leads to the planet Deneva, where Captain Kirk’s brother is stationed. A landing party beams down to the deserted planet where Kirk and friends encounter an angry mob, toward which they use deadly force. They soon find Kirk’s sister in law, screaming about creatures forcing them to build a ship. She dies unable to volunteer much more information.
The landing party soon encounter a flock of flying jelly pancakes, a strange new life form which was largely ignored by the crew, until one attaches to Spock’s back. It injects tissue in his body, painfully exacting its will on its new host, and Dr. McCoy is powerless to help. Spock manages to capture a live one, and attempts to study it. They are described as giant ‘brain cells’, which exist as a hive mind.
Aside from the fact that a single cell cannot exist at this size, as the ratio of surface area to volume would make it impossible for it to absorb enough nutrients, a brain’s decision making capacity is not located within one cell. It takes entire groups of neurons forming patterns along a network to have any information processing capacity. Is it possible that the hive mind was a single consciousness trying to perpetuate itself from planet to planet? These creatures may represent a biological version of the Borg…and one that is just as parasitic.
However, unlike the Borg, the flattened brain slugs were much easier to defeat. This is owing to them being specifically adapted to their environment. Through some scientific inquiry and theorizing by Spock and crew, the parasites were found to be susceptible to bright light, or more specifically, ultraviolet light. The initial full-spectrum treatment blinded Spock, but he was able to recover owing to an inner eyelid which protected his eyes from permanent injury. This adaptation was a vestigial remnant of evolving under the Vulcan sun.
The powerful influence exacted by the creatures, as well as the protective adaptations manifested in Spock, illustrate the context specific nature of adaptation and its role in targeted medical treatment. For example, when using chemotherapy to treat cancer, the procedure takes advantage of the fact that cancer cells are rapidly dividing. The drugs target actively dividing tissues in the body and destroy them, much like how the bright light destroyed the parasitic tissues within Spock. However, not all actively dividing tissues are cancerous; cells in our stomach and hair follicles regenerate rapidly. This is why chemotherapy causes nausea, digestive problems, and hair loss. Spock was blinded by the indirect effect that the medical treatment had on his eyes, but a more targeted treatment would have killed the unwanted tissues just as effectively without harming the body.
Finding specific chemicals able to ‘distinguish’ cancerous cells from healthy tissue is an ongoing goal in cancer research, and hopefully one without too much trial and error. Adaptations of an organism indicate to what an organism is resistant. Maybe researchers could consider to what environment the pathogen, parasite, or cancer cell is adapted, and then make its surroundings uninhabitable. The space parasites had never adapted to strong ultraviolet light, and it was to their detriment, while Spock’s evolutionary history on Vulcan is what saved him.