This is the time when comedies vanish.

On Tuesday, "According to Jim" has its final episode; the next night, "Scrubs" -- or, at least, its star — says good-bye. Each ran eight seasons, at a time when most situation comedies die young.

And 10 days later, "MADtv" has its finale. It lasted 14 seasons.

The good news is that networks are giving some shows enough warning to have a strong finale. "It's respecting the audience," said David Salzman, the "Mad" producer and co-owner. "The audience deserves that."

He's known for most of the season that this was the last one. As a result, many of the past stars will be back for the finale.

Successful shows should always get a strong farewell, argues "Scrubs" creator Bill Lawrence. "If you're on a show for six or seven years and you make somebody millions of dollars, I personally believe that you should get to end the show."

The people at NBC weren't so sure. "Scrubs" had only one season in the Nielsen top-30 and that was went it spent the entire year behind "Friends" on Thursdays, Then came 15 time-slot shifts in four years.

"We thought it was our last season every year for the past five years," Lawrence said, exaggerating for effect. "So the finale of the show has been written for about four-and-a-half years."

Except he almost didn't get to use it. Last season, with the writers' strike intervening, "Scrubs" had fewer episodes; NBC canceled the show and tried to pass off a fairy-tale fantasy episode as the series finale.

Fans fumed; so did Lawrence. Ironically, however, the show had always been produced by Disney, which owns ABC; that network gave "Scrubs" another year.

The trick was that "Scrubs" worked straight through, finishing all of this season's episodes before any of them aired. It knew that the last one would be a farewell for series star Zach Braff; it had no idea if this was also the end of the series.

Still, the basics could be handled. J.D. (Braff) could depart, to live closer to his baby. Previous characters could visit. And would viewers finally learn the janitor's name?

"I can tell you my name right now," said Neil Flynn, who plays him. "It's Zanzibar Buck-Buck McFate."

It's probably not; he borrowed that name from Dr. Seuss' "Too Many Daves."

Still, the character does get lots of input from the actor. "We've literally written in the script before, 'Neil Flynn says something funny,'" Lawrence said. "He's one of the best improv comedians working in our country."

That's been the spirit of the show. Lawrence hired clever people — Braff wrote, directed and starred in the 2004 "Garden State," a favorite with movie critics — and gave them room to work.

The result survived as other comedies wilted.

When the spring tryouts ended in late April for three shows, ABC had only three remaining half-hour sitcoms. There are only six on CBS, four on NBC, two on CW, zero (if you don't count animation) on Fox. That's 15, total; by comparison, ABC once had 18 by itself.

And that's just among sitcoms; sketch-comedy shows are also important. "Sketch is to comedy as short stories are to the literary form," Salzman argues.

They can do more, faster. "You have high relatability and humor and less problems with having to keep it tied down," he said.

Other sketch shows came and went, but only two have stayed. "Saturday Night Live" has been around since 1975; "MADtv" countered in 1995.

"We decided we would be the Uncola," Salzman said. "We would be rooted in pop culture and we would be very fast ... We had 14 or 15 segments in a 60-minute show."

The show created fun characters and launched gifted actors. It introduced Frank Caliendo, Nicole Sullivan, Orlando Jones, Alex Borstein, Aries Spiers and more.

Now some of them will be back for the finale. It's time for another comedy to vanish.