THE ZOO INSIDE YOU
One of the delights of science is its capacity for showing us that the world is not as it seems. A good example is the startling statistic that there are at least 10 times as many bacterial cells (belonging to up to 1,000 species) in your gut as there are human cells in your entire body: that "you" are actually an entire microbial zoo as well as a person.
You are 90% microbes by cell count, though not by volume -- a handy reminder of just how small bacteria are.
It has been clear for a long time that the microbes in your gut are not just passengers but colleagues that help with the digestion of food: releasing vitamins, breaking down toxins and metabolizing nutrients into more useful forms.
What's becoming clear from such experiments is that they are also vital to the immune system's capacity to fight infection. It's as if they train the body's defense forces.
For instance, breast-fed babies, whose gut microbes are dominated by creatures called bifidobacteria, are less likely than formula-fed babies to suffer not only from diarrhea but also from allergies later in life.