Organisms and micro-organisms a cohabitation between humans and bacteria and viruses. bacteria and viruses are in our environment (air, water, soil, objects, food). They are also present on the surface of our body on the skin and penetrate our body through the external orifices, nose, mouth, urethra, vagina and rectum. Thus, microorganisms are found in the mucous membranes of the nasal, oral cavities, lungs, ? sophage and stomach, intestinal tract and pelvic organs. Our body is therefore inhabited by microorganisms. This coexistence with some is very beneficial like the intestinal microbiota. The skin and mucous membranes form a barrier against pathogenic microorganisms in a healthy person. The captions on this illustration indicate the amount of microorganisms present in different parts of the body.