The newly-discovered organ, the interstitium, is a body-wide network of interconnected compartments that are filled with fluids that are supported by a meshwork of flexible proteins. It's found just below the skin's surface, and in the lining of our digestive tract, lungs and urinary system, and in surrounding arteries and veins, and in the fascia between muscles.
It seems to act as a shock absorber that stops tissues from tearing while the other organs, muscles and blood vessels go about their necessary functions, say researchers from the New York University School of Medicine, who made the discovery.
As a highway of moving fluid, the interstitium could also act as the channel that allows cancer to spread, they think.
And it could also explain why acupuncture works. The protein bundles within the interstitium generate electricity as they bend with the movements of the surrounding organs and muscles and could play a part in therapies such as acupuncture, the researchers say. The interstitium also seems to be involved in inflammatory processes throughout the body, which have been linked to a range of diseases from heart problems, diabetes, arthritis and some cancers.
Biologists have always missed the interstitium because they have focused on tissues and organs without seeing the spaces between, the researchers say. This is partly down to the way that science examines body tissue by treating samples with chemicals in a process known as fixing—and which drains away any fluid, which, essentially, is what the interstitium is.