How many sorts of good books are there? Too many to count. How many sorts of good books about science? Not good science books (such as The Origin of Species), but books about science? Only four, I think. There are books with a strong argument (The Selfish Gene); collections of slightly disturbing essays (The Man Who Mistook His Wife for a Hat); books that explain what science really is (Thomas Kuhn's The Structure of Scientific Revolutions); and books that no one reads but everyone feels they should (A Brief History of Time). The Spark of Life doesn't fit into any of these categories, nor does it persuade me that Frances Ashcroft has invented a fifth  books that tell you more than you want to know.

Every book is, in part, a reflection of its author  except, perhaps, when much of the work has been done by research assistants (Tertia Softley and Iara Cury get the credit here). I am sure, though, that this is Ashcroft's book. What I am not sure of is Ashcroft as a reader  she calls herself a "wordsmith", which isn't a good sign. One can't help but suspect that Softley and Cury did a good bit of the reading for her. Up and down the country there are now courses in creative writing. But who teaches uncreative writing?

I don't want to suggest for a moment that Ashcroft isn't a first-rate scientist. But this is a history book. It surveys our understanding of the role of electricity in the body, from Luigi Galvani (1781), who made dead bodies judder and shudder by electrifying them, through the work of Alan Hodgkin and Andrew Huxley (who studied the nerve cells of squid in the 1940s), to the revolution that resulted from the techniques established by Erwin Neher and Bert Sakmann (1980) for measuring infinitesimal currents in the body. These techniques laid the foundation for Ashcroft's own research career. But she doesn't seem to have spent long enough thinking about what historians do when they write history of science. So many obvious questions go unanswered: who funded the research? Where did the new paradigms come from? What was the relationship between pure science and practical medicine? Getting the Bodleian Library to let you handle the manuscript of Frankenstein no more makes you a historian than my visiting Ashcroft's laboratory would make me a scientist.

The Spark of Life isn't, however, organised as a history book. Instead it proceeds fairly logically through nerves, muscles, the heart, the senses, the brain, the mind. And we get lots of interesting examples  so many that it is hard to keep track of the book's structure  from sea urchin sperm, to fishing for electric eels, to the Japanese love of the poisonous pufferfish, and on to sharks eating underwater cables. There's plenty of "colour", too. David Clapham, who works on sperm, is "a Harvard scientist with a razor-sharp brain, a wicked grin and a salacious sense of humour"  unfortunately we don't get to hear any of his jokes. Then there's the "hilarious" story of how Ashcroft found herself hunting for an escaped frog in the dark at Cold Spring Harbor Laboratory. The frog was due to be wired up so that the impulses in its eyes could be measured, and the measurements depended on keeping it in the dark. The poor creature stood no chance.

I get impatient with books that survey a subject from A to Z, or from 1781 to 2011. At best you get a sort of fruit salad, sliced and diced, where I would prefer a single ripe pear. Instead of giving me four or five great ideas, or half a dozen classic experiments, Ashcroft gave me endless details, so that I began to feel as though I were preparing for an exam.

I did, however, learn one astonishing thing. The standard arrangement by which electricity passes through the body, from one cell to another, involves a chemical transfer. A positively or negatively charged molecule is passed through the cell membrane into a special receptor. It's almost as though I were to send an email to the postman, who would then print it out and post it through the door, where a little device scanned the incoming message and uploaded it to my home network. Or (to stick with electricity) as if the mains electricity was used to charge up a battery in my garden, which I then carried into the house to power my television. When I try to swat a fly, electricity doesn't just run from head to hand; it stops here and there on the way, a bit like airport travellers going through security  so much time saved, so much time wasted.

Is this packaging and posting process slow or fast? The cat who is trying to catch the mouse and the mouse who is trying to escape from the cat both rely on it. We don't have much experience of anything faster; and perhaps it is the inevitable price of having a cellular structure. In the 17th century the assumption was that "spirits" (we might say gases) moved up and down the body from head to heart to hand  the model was pneumatic, and it seemed ill-designed to explain the speed of a mouse's movement. Electricity, you would think, would be plenty fast enough, until you discover that it has to be packaged and posted every time it crosses a cell membrane.

It's here that medical malfunctions occur: the wrong packages or the wrong receptors, and you can end up with diabetes or some other life-threatening condition. And of course this introduces the possibility of an effective intervention that will trick the body into doing what it is supposed to do. As with so much work on DNA coding, the story turns out to be one of modest achievements, big grants (or so one must assume  the grants are never mentioned), and promises of a revolution in therapy that lies, as always, just around the corner.

 David Wootton's Galileo is published by Yale.