For decades, physicians could do nothing but watch their patients die. The breakthrough came from a series of accidental discoveries and brilliant deductions. 1. The Liver Diet Breakthrough (1920s)

In 1930, researcher William Castle conducted clever experiments feeding patients predigested meat and gastric juices. He deduced that a normal stomach secretes an that must bind with an "Extrinsic Factor" (the antipernicious anemia factor in food) to allow the body to absorb it. Patients with pernicious anemia, he discovered, lacked this intrinsic factor due to stomach atrophy. 3. Isolation of Vitamin B12 (1948) Pernicious anemia: MedlinePlus Medical Encyclopedia

Patients suffered from a slow, agonizing decline marked by severe pallor, extreme fatigue, a smooth and fiery red tongue, and irreversible neurological damage leading to paralysis, dementia, and death.