The Pennsylvania Medical Association — the well-funded organization representing the interests of doctors statewide — has come out with both barrels blazing against Senate Bill 25, a measure that would allow advanced-degree nurses to operate a practice not under the direct supervision of a licensed doctor. The organization argues that only doctors should be allowed to diagnose and prescribe treatments, or at least give them their stamp of approval. There’s merit to that argument, but I suspect it also serves a desire among doctors to preserve their “market share.” Allowing advanced-practice nurses and nurse practitioners to open up shops in all likelihood would make health care more widely available, particularly in under-served, poorer rural areas of the state.