Just recently, medical biologists may have discovered what is not only a new organ, but may also be the largest organ by volume in the human body.
It's called the 'interstitium', and is basically a lining under the skin layer and around many other vital tissues acting as a kind of shock resistant sheath.
It's made of little bubbles and passageways of fluid researchers are now calling 'interstitial fluid', all bound by a mesh-like network of strong and flexible proteins.
Basically, it's biological bubble wrap.
For 200 years, scientists have been seeing the interstitium very plainly in samples of human tissue, but have dismissed it as being an effect of tearing the tissue. In addition to this traditionally viewing tissue involves draining all fluid from it, which also destroys the interstitium's structure.
The interstitium seems to interface also with your body's lymph nodes and the lymphatic system (the circulatory system for your body's reservoir of lymph, the fluid that carries around your infection-fighting white blood cells), draining the interstitial fluid into the lymph system which may also explain why cancer can so easily spread to organs aside from the primarily affected organ. The discovery of this new organ can lead to huge breakthroughs in how we can treat and test for cancer, along with other advancements in diagnosing infections and diseases.