Bacteriophages were found to kill bacteria in the wreckage of World War I soldiers. A century later, the virus is drawing new attention because of its potential role in the human body. From the ocean to the soil, bacteriophages are almost ubiquitous. Now, one study shows that humans absorb up to 30 billion phages each day through the gut. Although the exact location of the virus is still unknown, recent data and other studies have prompted scientists to suspect that a large number of phages in the body - the "phage group" - may influence the physiology by regulating the immune system. A study of various animals from corals to humans found that the phage abundance in the mucus layer was more than four times greater than that in the surrounding environment, as was the case for phagosomes that protect human gums and gut. As it turns out, the outer sheath of the bacteriophage binds to mucus that is secreted by the body in large quantities and mucus together with water. Attached to the mucus makes the phage to encounter more bacterial prey. As a result, it has been demonstrated in a series of in vitro studies that these viruses protect the basal cells from possible bacterial pathogens and thus provide an additional immunological layer.