The main, or central, idea of the passage is Minot's liver cure experiment led to the discovery that a condition called pernicious anemia involves the inability to absorb vitamin B₁₂. How does the detail in bold develop the main idea?
In the 1920s, George Minot was searching for a cure for pernicious anemia, a then-fatal disease characterized by the body's inability to produce enough red blood cells. Minot began experimenting with feeding large amounts of beef liver to his patients—up to half a pound per day. Incredibly, the diet produced marked improvements. Why the medical miracle? As revealed by later research, liver contains high levels of vitamin B₁₂, which is essential for the production of red blood cells. People with pernicious anemia lack a glycoprotein called intrinsic factor, which helps the body absorb vitamin B₁₂ in the small intestine. As a result, their red blood cell numbers drop. Because Minot's patients could absorb only a tiny percentage of the vitamin B₁₂ in their food, they had to ingest large amounts of liver in order to survive. Today, people with pernicious anemia are prescribed B₁₂ injections so that they no longer have to rely on the "liver cure."