This is pretty disgusting.
And that's our speaker's point.
He wants to ram home just how absolutely degrading, humiliating, and surreal the destruction of the human body can be.
Within minutes, the body of a young man turns into a mass of aging sores – almost as a version of cancer moved through his body at warp speed.
Owen takes on a bitter, ceaseless realism towards the end of this stanza.
His speaker is deep in the memory of his own dream – and he's dragging us along for the ride.