So what is  microbe ?  Another term is microorganism, those tiny living things too small to be seen by the naked eye.  Is a virus a microbe?  Yes.  Is it alive?  That remains debatable.  As we have recently been overcome by just one, COVID-19, thought I'd deviate from the script and say few more things about viruses: Is the smallest of microbes. Walter Reed discovered the first human virus, a yellow fever virus, in 1901.  He proved that this ailment was transmitted by the bite of a mosquito.  That hospital in the DC area is named after him. 500 million rhinoviruses ( cause the common cold ) could fit on the head of a pin. There are ten viruses for every bacterium or archaeon. However,  viruses are 1000 times smaller  than bacteria or archaea. Some of you might not have previously heard of archaea, for Carl Woese only  discovered it in 1977 . Antonio van Leeuwenhoek discovered bacteria in 1676. As this is science day, a few more bits of info about  bacteria and archaea . They are