Until the 17th century, scientists thought blood was a one-way street. 

They believed blood was produced by the liver and consumed like food by the body's tissues.

 Until British physician William Harvey published a treatise so explosive, it was banned in England. He posited that blood was part of a circulatory system, continuously pumped through the body and recycled by the heart.

 In other words, when it comes to blood, what goes around comes around.

 Breaking new ground is never easy. You have to pull the rug out from under people. Shatter their reality. Ask more questions than you answer. 

It takes what Dr. Harvey called a love of truth. And a whole lot of intestinal fortitude.

 But it also requires faith. 

That the world won't come crashing down around you. 

That you won't be burned at the stake. 

And that this new reality is going to be better. 

Or at least truer than the one that came before.