Those warm hands will be spending a lot of time tapping keyboards. Already, Webcams and wireless computer technology mean that a single critical-care doctor in a command center can make rounds on dozens of intensive-care patients in hospitals miles away. On the horizon is a worldwide network of health care “nodes,” with instant information on anyone anywhere and keyboard-driven care crisscrossing the globe.

Dr. Hanson is a good writer  especially when he writes about patients rather than bionic limbs. One short description of a young woman confronting the aftermath of Hodgkin’s disease is particularly striking. But elsewhere his editors appear to have had some trouble keeping up with him: the book refers to bone marrow transplants for breast cancer as if they are still performed, and asserts that fluctuations in blood sugar cause diabetes, while it is actually the other way around. Whether descriptions of future technology contain similar errors is anyone’s guess: there are no references to check. But if your enthusiasm for the great beyond in health care can survive this caveat  and what is possibly a world’s record for misspellings of “principal” in a single document  then this is the book for you.

If, on the other hand, the whole idea just makes you shudder, you should turn to “The Big Necessity,” a story of the past, present and future of the simplest, cheapest, most all-round magnificent health care innovation of our time.

That would be the toilet, which many experts credit with a greater impact on disease eradication in developed countries over the last two centuries than any other device or drug on record. In a narrative that spans the primitive privies of China and India and space-age toilet factories of Japan, the British journalist Rose George tells a story every bit as complicated and mind-blowingly high-tech as Dr. Hanson’s.

In the West, the great 19th-century sewage systems are beginning to show their age, even as competing methods of water and sludge purification vie for primacy in cost and ecological friendliness. Meanwhile, 2.6 billion people in developing countries get along without toilets, and it takes the most delicate psychology to persuade them that they need them.

They do, believe me, for without toilets any disease that they have risks becoming yours. Never forget that the first great 21st-century pandemic, SARS, can be traced directly to faulty plumbing in a seventh-floor bathroom in Hong Kong.

In the name of research, Ms. George waded through sewers and checked out latrines all over the globe. On paper, she glides with rueful and articulate poise through the biology, ecology, physiology, psychology and basic hydraulics of her subject, always articulate and persuasive. Even if you are inclined to think health-care dollars should be put into titanium rather than porcelain, you will be hard pressed to put this extraordinary book down.