What substance was historically used by surgeons to block pain before synthetic local anesthetics were developed?

The correct substance that was historically used by surgeons to block pain before the development of synthetic local anesthetics is cocaine. Cocaine possesses natural anesthetic properties and was one of the first substances utilized for local anesthesia in surgical procedures. Its ability to numb tissue made it particularly useful, allowing surgeons to perform operations with patients fully conscious but not experiencing pain in the operated area.

While ether is often associated with general anesthesia, it does not provide the targeted pain relief that local anesthetics do; rather, it brings about a loss of consciousness. Aspirin, on the other hand, is known for its analgesic properties but does not function as a local anesthetic. Novocaine, though commonly recognized as a local anesthetic, is a synthetic derivative that came much later and would not have been available to surgeons prior to the advent of synthetic anesthetics. Thus, cocaine stands out historically as the primary substance used for regional anesthesia before more modern alternatives were introduced.