Scientists have learned to grow a living substitute for skin.

The new "skin equivalent," as it is sometimes called, can be grown in almost unlimited amounts starting with just a few natural skin cells. And it can be transplanted back to the donor of the natural cells with a high degree of success.

The work has been done so far in rats. But this new tissue could offer hope to humans who suffer often-fatal and almost always distorting, disabling burns over large parts of their bodies.

The first experinment in humans is just starting.

Three days ago, Dr. eugene Bell, the Massachusetts Institute of Technology biologist who discovered the new technique, created a tiny patch of artificial skin from his own cells and aplied it to his arm.

"It looks good so far," he said yesterday. "But this is very early.

"What we have, I want to emphasize, is something we think is exciting, something new that seems to work in animals, but that we have to prove out in well persons, then in burn patients.This is not ready yet for medical application."

Still, said Bell's coworker, Dr. H. Paul Ehrlich, "this looks very encouraging, because this skin is actually living skin, with viable epidermal and fibroblast cells" -- outer and inner skin cells.

What is more, Bell said, "the same technique, if it continues to succeed for skin cells, might very possibly be applied to grow other [types of] cells, too."

The technique is described in the weekly journal Science by Drs. Bell, Ehrlich and David Buttle of the noted Shriners' Burn Unit at Massachusetts General Hospital in Boston, and Takako Nakatsuji of MIT. m

It involves simply taking a small skin sample from a rat, then isolating the fibroblast, or connective tissue, cells that make up the inner part of the skin -- the dermis -- and growing them in a nutrient solution. The new cells harvested are then combined with collagen -- the main protein of skin, taken from the rat's tail -- to gradually form a "matrix" or latticelike bed.

Then, a few days before transplantation, some of the rat's epidermal or outer skin cells are applied to the lattice, so the ultimate product is indeed a living skin closely related though not identical to the donor's own skin. The scientists working with in variously call it "skin substitute," "skin equivalent," "artificial skin" or just "skin."

In treating burns, some of the patient's own skin is commonly removed and transplanted to cover the burned areas.

"But in the extensively burned," said Ehrlich, "if the burn covers more than 50 percent of the body, or perhaps even less, there just isn't that much skin left to use."

Removing it may also further traumatize a patient already in poor or precarious shape.

When a burn isn't covered with the patient's own skin, and sometimes when it is, thick sections of scar tissue form and eventually shrink, pulling the surrounding skin and underlying tissues out of position. This can cause severe distortion and crippling.

The new technique has been used in 52 grafts in rats -- grafts measuring up to four-tenths of an inch long and sometimes covering 10 to 15 percent of the body altogether, and there has been no rejection or sloughing off of the new skin. Eighty percent of the grafts have kept their original size and shape for up to 13 months so far.

"What seems to happen," Ehrlich said, "is that some of the cells in the graft move to the normal adjoining skin, and some of the cells in the normal skin move the graft. In time the whole area is remodeled. This is a normal process. Normal skin is not static. There is breakdown and new synthesis all the time."

There have been other attempts to produce skin substitutes or artificial skin, and some promising ones are still in progress. But none has yet come into accepted use.

The new technique, like many in science, was discovered by accident.

"We were studying the basic biology of fibroblasts," Bell said. "We were examining the contractility of these cells that make up the dermis and seeking a quantitative assay, a measurement. We decided to try something a little more tissue-like, so we incorporated some cells into a collagen matrix.

"We had an unexpected result. The cells grew into something that looked like skin."