The suspect, in handcuffs, was sitting on the ground and leaning against a cruiser, his face bloody from a struggle with police.

When the paramedics got close enough to put a neck brace on him, he started coughing and spewing blood in the face of paramedic Carlos Nieto.

"Cut," yelled the director.

The scene wasn't real, it just looked that way. It was part of a crossover episode that will start Friday at 9 p.m. on NBC's "Third Watch" and continue at 10 on the network's "Medical Investigation."

The story centers on a jewelry store thief who is AWOL from the Army and displaying unusual symptoms of an unknown contagious disease that is spreading fast. His accomplice, who is also likely to be infected, is on the run. The team from "Medical Investigation" are charged with deciphering the deadly scourge.

It's not the first time that Anthony Ruivivar (who plays Nieto) has been sprayed with fake blood.

"We use gallons of blood on this show," said Ruivivar during a break in filming on the eastern end of Canal St. "Because we use so much of it, we have our own special blends of blood."

It's very important to get the right blood for the right occasion.

"We have a special mouth blood for Anthony," said key makeup artist Andrea Miller, also known as "the blood lady."

"It's slightly sweet and it has a nice flavor because it goes into Anthony's mouth," she said, "and I gotta keep Anthony happy. He's my baby."

The mouth blood is sweetened with Kayro syrup.

The crossover episode is a staple of sweeps periods, when stunner plot twists and guest actors - Wyclef Jean guest-stars in the crossover - are hauled out in an attempt to rise above the cacophony.

For the casts of "Third Watch" and "Medical Investigation," it's a sign that the network is investing in their series, which is especially positive for freshman drama "Medical Investigation."

"I think it signifies that NBC's got some pretty good faith in both of us right now," said Neal McDonough, who plays Dr. Connor on "Medical Investigation."

"Does this mean we're not being canceled," joked Molly Price, who plays Faith Yokas on "Third Watch."

"I hope we've made it.

"God, we've been on the air for six years. They've moved us all over the map and no matter what they do to us, we always have this hard-core, vigilantly loyal audience. We're like a cockroach. They just can't kill us."

McDonough and Price are in a car to keep warm, no easy feat when filming on location in New York during subfreezing weather.

But the elements, not to mention disgruntled New Yorkers unhappy that they must navigate yet another film crew, provide priceless atmospheric detail.

"We were shooting [in Chinatown]," said Ruivivar, "and a truck pulls up and a guy opens up the truck and it was filled with dead pigs."

Josh Stewart, who plays Officer Brendan Finney on "Third Watch," adds: "Shooting on the streets of New York, especially shooting a cop show, you can't duplicate the energy that comes from the streets and the city and the people."

Ruivivar also had to travel to L.A. to shoot his scenes for the "Medical Investigation" episode.

"They have it so easy in L.A.," he said. "The weather's beautiful. They're on the lot. They're running around in golf carts. Craft services has wheat grass. We're in [freezing] weather battling the elements. They were bitching because they had to shoot in the rain one day. I'm like, 'Are you out of your mind?'"