Of course I’d long known that I was playing host to a massive collection of parasitic organisms, but I didn’t much like being reminded of it. By cell count, humans are approximately 50 percent microbial, meaning that about half of the cells that make you up are not yours at all. There are something like a thousand times more microbes living in my particular biome than there are human beings on earth, and it often seems like I can feel them living and breeding and dying in and on me.
