To pathogenic microparasites (viruses, bacteria, protozoa, or fungi), we an
d other mammals (Living organisms at large) are Little more than soft, thin
-walled flasks of culture media. Almost every time we eat, brush our teeth,
scrape our skin, have sex, get bitten by insects, and inhale, we are confr
onted with populations of microbes that are capable of colonizing the mucos
a lining our orifices and alimentary tract and proliferating in fluids and
cells within us. Nevertheless, we rarely get sick, much Less succumb to the
se infections. The massive numbers of bacteria and other micro- and not-mo-
micro organisms that abound and replicate in our alimentary tract and cover
our skin and the mucosa Lining our orifices normally maintain their commun
ities in seemingly peaceful coexistence with the somatic cells that define
us. Why don't these microbes invade and proliferate in the culture media wi
thin the soft, thin-walled flask that envelops us? Why don't they cause dis
ease and Lead to our rapid demise?