How do blood transfusions work?

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? Bill Schutt explains the history of the life-saving procedure. [Directed by Hype CG, narrated by Addison Anderson, music by Gabriel Maia].