Excerpt from The Body by Bill Bryson, plus links to reviews, author biography & more

In theory, it ought to be fairly straightforward, particularly because an artificial blood wouldn't need to do most of the many things real blood does except carry hemoglobin.

"In practice, it's proved to be not so simple," says Doctor with a fleeting smile. He explains the problem by likening red blood cells to those magnets that you see picking up cars in junkyards. The magnet has to latch on to an oxygen molecule in the lungs and convey it to a destination cell. In order to do that, it has to know where to take the oxygen and when to release it, and above all it mustn't drop it en route. That has always been the problem with artificial bloods. Even the best- made artificial bloods occasionally drop an oxygen molecule, and in so doing release iron into the bloodstream. Iron is a toxin. Because of the extreme busyness of the circulatory system, even an infinitesimal accident rate will quickly mount up to toxic levels, so the delivery system has to be pretty much perfect. In nature, it is.

For more than fifty years, researchers have been trying to make artificial blood but, despite spending millions of dollars, are still not there yet. Indeed, there have been more setbacks than breakthroughs. In the 1990s, some blood products made it into trials, but then it became evident that patients enrolled in the trials were having alarming numbers of heart attacks and strokes. In 2006, the FDA temporarily shut down all trials because the results were so bad. Since then, several pharmaceutical companies have abandoned the quest to make a synthetic blood. For now, the best approach is simply to reduce the volume of transfusions. In an experiment at Stanford Hospital in California, clinicians were encouraged to reduce orders for red blood cell transfusions except when absolutely required. In five years, transfusions at the hospital fell by a quarter. The result was not only a $1.6 million saving in costs but fewer deaths, quicker average discharges, and a reduction in post-treatment complications.

Now, however, Doctor and his colleagues in St. Louis think they have nearly cracked the problem. "We have nanotechnology at our disposal now, which wasn't available before," he says. Doctor's team has developed a system that keeps the hemoglobin inside a polymer shell. The shells are shaped like conventional red blood cells but are about fifty times smaller. One of the great virtues of the product is that it can be freeze- dried, enabling it to be stored for up to two years at room temperature.

At the time I met him, he believed they were three years away from trials in humans, and perhaps ten years from using it clinically.

In the meantime, it remains a slightly humbling reflection that about a million times per second our bodies do something that all the science of the world put together so far cannot do at all.

Excerpted from The Body by Bill Bryson. Copyright © 2019 by Bill Bryson. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.