[brownstone.org]
What Killed Informed Consent?
It wasn’t until the 1850s that English Common Law started to reflect worries about injuries incurred from surgery without proper consent. The courts increasingly interpreted a physician’s failure to provide adequate information to the patient about his or her treatment as a breach of duty. This trend culminated in the 1914 case of Schloendorff v. Society of New York Hospital, which was the first to establish that the patient is an active participant in the treatment decision process. The judge in the case, Justice Benjamin Cardozo, stated:

…every human being of adult years in sound mind has a right to determine what shall be done with his own body; and a surgeon who performs an operation without his patients consent commits a battery for which he is liable in damages.