If we were to find ourselves in a sealed chamber with all we needed to eat, drink, and breathe, we would still soon expire. Our own waste products - especially the carbon dioxide we exhale - would do us in.

For the cells of the body, a similar situation exists. They need to have their cellular wastes removed or they too will die. Of course, cells will die in any case, but under good conditions they will (except for brain cells) be constantly replacing themselves through ongoing cell division, albeit at a different rate in different structures. Obviously, then, if the cells of the body could undergo cell division indefinitely, we might contemplate a much expanded life span, with fewer age-related problems.

As an experiment, a French surgeon, Dr. Alexis Carrel, immersed pieces of a chicken heart in a saline solution, a solution that contained various minerals in the same concentration as found in chicken blood. He disposed of the waste products daily, and was able to keep the cells of the chicken heart alive for 28 years. Needless to say, that was well beyond the life span of any ordinary chicken.

Now, it is obvious that, while most of us would love to have our bodies live on well past the normal life span, we would not wish to achieve this objective at the expense of living in a saline solution, in a giant petri dish, in pieces.

Not to worry, that will not be recommended. As it turns out, the success of Dr. Carrel's experiment lay partly in the fact that fresh cells had been inadvertently added to the culture that was keeping the heart cells alive.

However, the experiment does explain why the cells of an older person, which contain more waste products, divide more slowly and fewer times than do cells from an embryo that are less burdened with waste.