When I reviewed “The Erlenmeyer Flask” a few weeks ago, I discussed the notion of the alien corpse or “wellspring” as a kind of Pandora’s Box. Use of the alien corpse’s DNA in scientific experimentation would mean -- in the universe of The X-Files --a brave new world, one with infinite variations, and infinite capacity for good and evil applications.

Chris Carter’s episode “The Host” also involves, at least implicitly, a Pandora’s Box of another brand.

In “The Host,” Mulder and Scully investigate a strange mutant spawned in the real life radioactive horror of Chernobyl and conclude, chillingly, that it may be only the first such creature “born” out of man’s mistakes and short-sighted treatment of the environment around him.

Or as the episode’s dialogue makes plain: “Nature didn’t make this. We did.”

In this case, nuclear power is the Pandora’s Box, and the thing that, once “opened,” spawns unpredictable terrors.

Beyond utilizing the horror of Chernobyl as the monster’s point-of-origin in “The Host,” this second season story of The X-Files works so splendidly because it gazes at a kind of corollary for the Chernobyl accident.

In particular the Chernobyl accident involves possible mismanagement -- or human error -- in a setting of vital importance to man’s communities. In “The Host,” the topic isn’t nuclear power, but the ways that modern civilization removes or disposes of biological waste on an industrial scale. In other words, the vast sewage plant of “The Host” replaces the nuclear plant at Chernobyl as ground zero. It is a stand-in for that locale.

Accordingly, “The Host” veritably wallows in tons of sewage, waste, and other unpleasant side-effects of human biological processes. At least three crucial scenes are set near toilets (aboard the Russian freighter, in a home bathroom, and finally, in a campground outhouse). The tacit connection to Chernobyl is that the accident which occurred there in the eighties also involved a modern response to a basic human need, but for power (and thus heat and light), rather than a place to extrude waste.

In addition to Mulder’s several nauseating trips into raw sewage, “The Host” terrifies because of the absolutely unpleasant or unsavory nature of its monster, the “fluke man,” a humanoid with a sucker for a mouth, and rolls of loose fat for a trunk.

The Fluke Man is decidedly hideous in appearance, but even more terrifying in his behavior. He injects his victims with his young, his larvae, so that human beings become host to the parasites before dying a horrible death.

One particularly harrowing scene in “The Host” finds a hapless sewer worker throwing up a worm while taking a shower. And the episode’s big “jump” moment involves another “baby” worm poking its nose out of a corpse during an autopsy conducted by Scully.

Although I haven’t gone back and watched every X-Files episode preceding “The Host,” I’m pretty certain that no other episode yet produced has traveled so far down the line of biological or body horror, and featured so many absolutely grotesque “ick” moments.

And, not incidentally, this episode re-states The X-Files Gothic thesis about the Romantic response to Enlightenment. Here, science creates monsters. The age of “rationalism” gives rise to magic, mystery and inexplicable new terrors. A tabloid contending in sensational (and thus Romantic…) tales of monsters and mayhem offers the clue which allows the scientist, Scully, to solve the episode’s mystery.

Taken as a whole -- or in disgusting pieces for that matter -- “The Host” remains one of the X-Files’ greatest and most memorable “monster of the week” stories. It is scary because the Fluke Man is grotesque and monstrous, but even more so because it goes where few (TV) horror stories might be willing to tread: into the facts regarding human waste disposal in a modern setting.

With The X-Files still officially shuttered, Mulder is relieved of his wiretap surveillance assignment and asked to look into a bizarre murder case in Newark, New Jersey. In particularly, a body is found in the sewers with a strange bite mark, and a Russian tattoo.

While Mulder hunts the murderer -- a giant fluke worm -- Scully determines that the victim may have come from a Russian cargo ship carrying contaminated water from Chernobyl.

Digging deeper, Mulder and Scully find that the adult fluke-worm mutant -- part parasite and part man -- is using human bodies as an incubation place for its young. They are faced with the specter then of a whole colony of such Worm/Human Mutants…

On April 26, 1986 a disaster of unprecedented proportions occurred at Nuclear Reactor 4 in the Chernobyl facility.

Over four hundred times the amount of radioactive material that was released in the Hiroshima bombing in 1945 was dispersed into the atmosphere over the Ukraine. The area around Chernobyl was evacuated as workers struggled to contain the nuclear meltdown, but the long-term effects of the accident were only beginning.

For instance, the Pripyat River -- which supplied drinking water to 2 million people in Kiev -- was contaminated, as were fish in the area. Citizens were exposed to the high level of radioactivity in the immediate vicinity, and began to experience higher incidences of Thyroid cancer. The same poisoning occurred with local wild-life.

Chernobyl is a terrifying place where science fiction meets science fact, and in a very unfortunate manner too. Deformities of a horrendous nature were detected in animal and human births after the nuclear accident, and a new kind of “black fungi” was even seen, years later, thriving inside the abandoned reactor walls. Was it a new kind of life?

Chris Carter’s fluke-man does not seem so far-fetched or outrageous an outcome when one considers all these gruesome details, and once again The X-Files plumbs real-life fears to make its fictional horror feel more realistic and immediate.

The environmental and human cost of the Chernobyl accident is horrible enough, but in some sense, one might call it “distant” from our national concerns. The meltdown happened in the Soviet Union, after all, and some eight years before the second season of The X-Files was commissioned. But cannily, Carter relocates a Chernobyl-style horror to another vast, industrial locale, and also one of crumbling infrastructure: our sewers and sewage plants.

Before it is done, “The Host” features obsessive views of backed-up toilets, sewage plants, flooded tunnels, out-house shit pits, and even men knee-deep in human waste. The obsession, rather clearly, is on the underbelly of modern civilization.

Today, we flush our toilets, and don’t really think about anything beyond that local outcome. But indeed, there is an entire industry -- invisible to most -- dedicated to treating and disposing of that waste once it leaves our homes. The toilet is actually only the beginning of a long journey. “The Host” garners so much of its ability to disturb by shining a light on the things we’d rather not know about the end results of our normal biological processes.

In some respects, this is the very key to crafting successful horror: investigating something real and disturbing, and then adding a fictional horrific element beyond the reality of location. The Texas Chainsaw Massacre (1974) does the same thing, after a fashion, by frequent references to the local slaughterhouse and the incidents that occur inside. That real “terror” is then connected with a fictional one, in this case a cannibal family. But the uncomfortable aspects of the slaughterhouse set audiences on edge, and sow anxiety. In “The Host,” the sewage plants and other “bathroom” imagery perform an identical function. They augment the terror of the actual monster to a considerable (and sickening…) degree.

Part of what makes “The Host” work so effectively is its decorum-shattering approach to facets of life we’d rather not talk about, at least in polite company. The Flukeman hides in an outhouse shit pit, unseen and undetected, but the thought of that fanged thing just waiting down there for an unsuspecting person to make a “deposit” is almost too much to bear, especially considering how vulnerable people are when they sit on a toilet.

In some ways, this episode’s focus on waste -- from the stopped-up toilets on the Russian freighter to the monster in the outhouse waiting to strike -- is as every bit convention-busting as the series’ most notorious episode: “Home.” “The Host” makes us face things we’d rather not gaze at.

In terms of X-Files continuity, this story introduces Deep Throat’s successor X, if only as a voice on the telephone, and establishes the re-opening of The X-Files. There’s also a great scene here for Assistant Director Skinner (Mitch Pileggi), when he acknowledges openly that closing the unit was a mistake. This dialogue reveals to viewers that Skinner is not just a bureaucrat following orders, but someone who Scully and Mulder can at least begin to trust.

Next week, I’ll cover both parts of the epic second-season two-parter: “Duane Barry/Ascension.”