What happens if you're injected with the wrong blood type?

Dive into the history of the life-saving procedure of blood transfusions and how it has evolved since the 17th century.

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In 1881, doctor William Halsted rushed to help his sister Minnie, who was hemorrhaging after childbirth. He quickly inserted a needle into his arm, withdrew his own blood, and transferred it to her. After a few uncertain minutes, she began to recover. What made this blood transfusion successful?