Bleeding Patients
| Field | Medicine |
| Went Obsolete | 19th Century |
| Made Obsolete By | Germ theory |
| Knowledge Assumed | Anatomy, especially the pulmonary system |
| When useful | Medical treatment |
Bloodletting was once a popular medical practice, used to treat most ailments. Doctors would withdraw blood from the patient, sometimes in large amounts, in the hope of curing the patient. In the 19th century, though, it fell into disfavour and was phased out as other, more effective remedies were applied.
Note that bloodletting is not entirely obsolete: ailments such as Polycythemia Vera and Hemochromatosis are still successfully treated through phlebotomy (as bloodletting is now known), but this could arguably be considered a separate skill due to the change in method and instruments used.
Donating blood is like bloodletting. It just isn't claiming to cure anything.