The Body: A Guide for Occupants

Almost everything concerning the body contains an element of wonder. It is made of 35 trillion microscopic cells, and an equal number of microbes inhabit it. Each cell is controlled by a chemical, DNA, that contains the complete set of instructions for the construction and regulation of the entire body, bunched up in microscopic strands which, if unfurled and stretched out end to end, would span a distance of 10 billion miles, well past the outer planets. 

The lungs inhale 20,000 times a day in nearly flawless perfection despite having to share an intake tube with swallowed food. The immune system can remember a previous invasion by microbes and respond promptly and thoroughly years later, should that pathogen re-enter the body. Hot days or cold, sprinting or lying still, the body maintains its internal temperature to within one degree. 

On nearly any topic of anatomy, physiology, and medicine, the facts contain astounding information. The life of a human body is wondrous even during its ordinary activities—walking, thinking, eating, sleeping—and makes for an ongoing, continuous source of interest.