Students of history know that over the millennia, great civilizations crumbled not from without, but from within. The Visigoths may have crushed the Romans in A.D. 476, but long before the Roman Empire had begun to disintegrate internally, its social fabric slowly shredded apart -- and ultimately it became a paper tiger unable to sustain itself. In our own lifetime, it's quite apparent that we are witnessing an increasingly rapid and equally worrisome descent in the moral mean.

Here's one spectacular, depressing example. In the 1970s, one of the most celebrated family shows on TV was "Little House on the Prairie." One of NBC's most durable series, its audience would trounce today's television "hits" because back in those days, "family" TV shows were watched by the family, not just the youngest offspring.

The lead role was played by Michael Landon, but the show also gave rise to another star, the gawky, pig-tailed child named Melissa Gilbert as Laura Ingalls, or "Half-Pint," as she was lovingly called by Pa Ingalls. In recent years, she has starred mostly on family friendly shows like "Touched by an Angel" and "7th Heaven."

Perhaps this is a classic example of how pathetically low our society's morals have fallen in 25 years: Melissa Gilbert just guest-starred on the FX cable network's grotesque show "Nip/Tuck." Are you ready for this? As a woman needing to have a nipple replaced ... because her dog bit it off ... during sex.

I'm not kidding. I wish I were.

It was somehow not enough to have a little light fun of sex with a cow (ABC's "Boston Legal"), or sex with a horse (on Fox's "Keen Eddie") or even violating a parrot with a finger (on the aptly named UPN show "Shasta McNasty"). Now it's bestiality with the family dog as the punch line. Lassie and Rin-Tin-Tin, be glad you're dead.

Gilbert's husband returns home from Iraq to discover his wife is enraptured with a whole new definition of "puppy love." He screams at her in disgust that he failed to expect she would turn into a "faithless, demented whore," a special breed of floozy to be sure, given she used peanut butter to seduce the family pooch into the sack.

To complete the circle of sleaze, the husband vengefully dumps the dog, now a lifeless heap, out of a duffel bag in front of her. This being a graphic show about surgery, we see -- we have to see -- Gilbert's bare breast (albeit covered by a plastic wound) as they prepare her for a new nipple.

Why did she do this? Is the "wholesome" tag such a scarlet letter in today's Tinseltown that it requires this level of penance? Perhaps there's even more to it. Until recently, Gilbert was president of the Screen Actors Guild, which has fought proposals to strengthen protections against televised indecency. Gilbert couldn't have taken a more public stand (in this case, in the prone position) than this disgusting stunt.

"Nip/Tuck," television's most overwrought sleazefest, is beginning its fourth season of plastic surgery and gaudy immorality with a load of new guest stars clamoring for seats on the bandwagon, but the same perverse drive to shatter every barrier of good taste. It's so graphic, violent and sexually repulsive that one prison banned its inmates from watching it. But it's available to millions of impressionable children on the cable or satellite TV systems in their homes.

And TV critics continue to applaud every new outburst of wickedness. The Hartford Courant has raved that "no show has been as consistently audacious, finding the very edges of taste and acceptance each week and using every power of its extended cable status to leap beyond them." The Palm Beach Post lovingly described it as a "shocking, sexy, graphic, funny, wildly over-the-top, I-can't-believe-what-I'm-watching drama."

They aren't looking for artistic excellence. They are looking for the fastest path to subversion, a rollercoaster ride to the depths of excess. "Nip/Tuck" can meet them there with great enthusiasm.

Up next on "Nip/Tuck" is Rosie O'Donnell, and it wouldn't be worth the guest-starring role without Rosie's character having sex with Dr. Christian Troy, the show's stud muffin. TV Guide has already spurred O'Donnell to recount the filming of the "absolutely hilarious" sex scene, how the actor playing Dr. Troy was naked except for a sock and she decided to go topless, and how her lesbian partner loved watching every minute.

And Hollywood's loving it. "Nip/Tuck" creator Ryan Murphy is popular enough that he's preparing another project for FX called "4 oz.," named for the average weight of a flaccid penis. It's a drama about a transsexual sportswriter with a wife and two teenage sons. There's no cast yet, but he claims his phone "is ringing off the hook" from A-list stars who he says shall remain nameless. The wages of preposterous sin are rich indeed in today's Hollywood.