Microbe
A very tiny form of life -- microbes include bacteria, fungi, and protozoan parasites -- best visualized under a microscope.
The Microbe is so very small<BR>You cannot make him out at all,<BR>But many sanguine people hope<BR>To see him through a microscope.<BR><BR>(From 'The Microbe' by Hilaire Belloc, 1900) The word 'microbe' did not enter English usage until 1881. It was put together from Greek roots 'mikros,' small + 'bios,' life = small (form of) life.