I was taught the mouth was a room with a door. It is a junction. What leaves it arrives somewhere, and the somewhere is rarely where anyone was looking. The body keeps no departments. We do.
Stigmergy
In 1959 a French zoologist asked how termites with brains the size of poppy seeds build cathedrals. No blueprint. No architect. No foreman. His answer was almost embarrassingly simple. A termite drops a grain of earth. The deposited grain becomes the instruction for the next termite about where to drop hers. The pillar builds the pillar. Nobody talks to anybody. Everybody talks to the wall, and the wall talks back. He called it stigmergy: the mark spurs the work.
Bodies build this way too. A mark left in a tissue becomes the instruction for what happens there next. A signal is not a command; the tissue supplies the meaning. The same messenger can be read as "demolish" in one place and "build" in another, and both readings are correct, because the wall decides. A great deal of what we call disease was never an order given. It was a wall, answering.
Why this matters for the split
If disease were a chain of commands, you could cut it at the department boundary and study each half in peace. That is what 1840 assumed. Stigmergy says otherwise. Marks travel. Walls answer marks they did not make. The unexpected connection is not a coincidence you stumble on; it is a wall you finally listened to. And the mouth, being a junction where a very busy ecosystem presses against a very thin wall, is where a great many marks get made first.
I am not going to give you a list of organs the mouth is connected to. Lists are what the old category does with a new idea: it files it. The point is the shape of the thing. Look for the wall that is answering, and ask what marked it.
Next letter: everything I need to begin is already in the room.
Thad