Auto-immune diseases вЂ“ a category including allergies in which your own immune system works against you вЂ“ remain poorly understood and largely incurable. While techniques that harness the bodyвЂ™s immune response are proving successful against some types of cancer, in other areas we remain woefully stumped.

Little wonder, then, that our understanding of so many illnesses remains murky. Every individualвЂ™s immune system is both unique and changeable: it varies if you are stressed or exhausted. You could call together all the brainiest people who are alive now or have ever lived and endow them with the complete sum of human knowledge, and they could not between them make a single living cell, never mind a replicant Benedict Cumberbatch.вЂќДЄnd there isnвЂ™t just one вЂњimmune systemвЂќ. But as Bryson writes: вЂњIt hardly matters. Calcium, phosphorus, potassium and a smattering of rarer elements make up the rest. It gets pricier when we get to carbon, which costs ВЈ44,300 for the 30lbsвЂ™ worth we typically contain.

To run the numbers: you are 61 per cent oxygen (ВЈ8.90) and 10 per cent hydrogen (ВЈ16), mostly bound up together to make water. As The Body makes vividly clear, we are both mundane and miraculous: composed of a bunch of mostly everyday elements, pieced together in astonishingly complex systems that scientists today are still a long way from understanding. Or at least a human of the same dimensions as Benedict Cumberbatch does, according to a Royal Society of Chemistry calculation that Bryson cites.

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