Now, let's be clear, we didn't just blatantly ignore the presence of a human body part for the past thousand years. We were always aware that the interstitium, itself existed, but it was accepted as simply a layer of fluid and vaguely-connected fibers lying between the skin and all of the other organs. Just recently, however, researchers claimed that they found proof that this system is actually a fully-connected, single organ in the same sense that the skin is.
For the record, this shouldn't completely blow you away, as a similar discovery also occurred just over a year ago.
In terms of function, the interstitium is a network of tissue and pathways throughout the body and containing any fluid of the body that's otherwise outside of cells or other vessels (such as lymphatic or blood vessels). This is nothing new, but the new research suggests that the extent of this interconnectivity has large implications on exactly how much the separate systems of the body communicate together.
The preliminary findings are (vaguely) suggesting that this new classification of the interstitium as a more-widely connected organ may help us to understand certain things such as the mechanism of acupuncture or the spread of cancer better.
The main reason for wanting to write this, however, it to precaution everyone that all of these findings are preliminary. It won't be long before groups and individuals begin to emerge claiming to be altering, adjusting, or otherwise treating health conditions directly via the interstitium. With very little research on the implications of this organ, let alone more than minimal proof that it even is an organ yet, everyone would be wise to be critical when hearing the upcoming gospel regarding the system and to be wary about miracles to be done with it. We may, in fact, get some very exciting discoveries out of this, but let's make sure any information coming our way is concrete.