All the coins minted in the United States say it: E pluribus unum; out of the many, one. It is a great general principle, the idea that from a vast and diverse group of individual objects there should arise a single, unified entity.

On the coinage, of course, the individual objects referred to are people, while the single entity is the nation. However, the concept extends far into other fields. In physics, for example, Albert Einstein spent most of his last 30 years seeking a "unified field theory," which would provide a single underpinning for the physical laws of nature. From this he hoped that all the myriad phenomena that we see in the universe could be explained and calculated.

Einstein failed. He does not seem to have been too upset by that failure, and perhaps he never expected to succeed. As he himself said, he could afford to spend the last third of his life in the search for a unified field theory, because his own reputation was secure. A younger scientist, lacking Einstein's great body of earlier accomplishment, dare not take the very great risk of failure.

Einstein is often thought of as the first scientist to seek unity in all of physics. He was not. Two and a half centuries earlier, his great predecessor, Isaac Newton, shared the same obsession at a time when science, alchemy, and philosophy were not clearly distinguished. Newton was so far ahead of his time that in 1706 he speculated that the behavior of atoms ("the small particles of bodies," as he described them) and the movements of large objects, such as planets, should logically be controlled by a single set of laws involving "the attractions of gravity, electricity, and magnetism," the only forces he knew about. But he had foresight enough to write, "there may be more attractive powers than these. For Nature is very constant and conformable to herself." It took 230 years before scientists could add the subatomic "strong force" and the "weak force" to Newton's list.

The search for the unification of all physics still goes on, in what is usually called a TOE - Theory of Everything. Of course, we may be missing vital information about Nature's laws, just as Newton and Einstein in their own times lacked crucial facts. Maybe it will take another two and a half centuries before we even come close to unity in physics. In the meantime, however, we can seek unification in other places. And, in fact, there are subjects other than physics where I personally would rather see unification.

For example, in medicine. You and I consist of assemblies of about a thousand trillion separate cells. But - e pluribus unum - these cells all work together, allowing me to sit here and think, while at the same time I am unaware of breathing, or digesting, or my eyes blinking, or the blood circulating around my body, or of all the actions of individual nerves and muscles that must conspire to enable me to type (poorly) this sentence.

The human body seems like a wonderful example of perfect unification. Until sickness or old age comes along, it is. At the point, however, when things go wrong we call upon outside assistance in the form of medications to restore our well-being; and it is here that any semblance of unification is lost. Medicine is not a unified discipline, as any doctor will be the first to admit. Our thousand trillion cells, evolved over a billion years to work harmoniously together, are interrupted in their cooperation by drugs intended to address a single problem.

Often, the drug addresses that single problem wondrously well. But the integrated nature of the human body guarantees that's not all that a medicine - any medicine - does. Let's take as an example one of the most widely used and reliable drugs in the physician's arsenal: aspirin. Aspirin has been used for over a century, as a painkiller and to reduce fever and inflammation. It used to be almost the only medication available to treat the pains of arthritis. More recently, it has been found to serve as an anti-coagulant and "thin the blood," so that many doctors recommend to older people an aspirin every other day as a protection against heart attacks and strokes.

So far, so good. But what else does aspirin do to the finely balanced cooperative system of the human body? The honest answer is, we don't know. Some of the possible side effects of aspirin have become clear after a century of use, and a doctor can warn of possible ulcers, upset digestive systems, allergic reactions, and, in the case of aspirin overdose, ringing in the ears, dizziness, dimness of vision, and nausea.

All this, for a drug that we have been using since the 1890's. What about the hundreds of new drugs that come on the market every year? Most of us don't read the printed list of possible side effects that come with a filled prescription. If we did, maybe we would think twice before swallowing that pill. And even if we did think, make a conscious decision, and go ahead because the side effects listed seem tolerable and acceptable, still we might not be safe. The horror story of thalidomide, forty years ago, drove home the point that the effects of a single drug on the infinitely inter-connected and integrated complex that constitutes a human being cannot be predicted. As for the interactions of several drugs - and many older patients are taking five or six, every day - no reputable physician will even speculate on the consequences, possibly highly nonlinear, of drug combinations.

Until very recently, the tools to attempt unification in medicine did not exist. Now, with medical research workers able to study the effects of a drug, or even combinations of drugs, on the activity of single genes, and with the complete cataloging of the whole of the human genome, a basic understanding at the cellular level can at last be attempted. Of course, even when we know in detail what is going on within the cell, we will still be a long way from understanding the effect of medications on the integrated, almost infinitely complicated mosaic of cells, chemicals, reactions and processes that make up the entire human body. However, even though it lies far in the future, I see whole-organism understanding and unification as the ultimate objective of medicine.

E pluribus unum: perhaps it should be written on every medical prescription pad, just as today it is written on every coin.

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