Bacterial world

If a visitor from another planet were to analyse our bodies, they'd conclude that we were only 10% human. That's because around 90% of the living cells in a human body are made up of bacteria, some of the smallest and most numerous living organisms on Earth. Yet, in spite of their abundance, we find it difficult to see any of them without the aid of a powerful electron microscope. On the head of an apparently perfectly clean pin, it is only when we magnify 10,000 times that the size of the bacteria becomes clear and we can finally see the colonies.