Holding a Real Spleen!

But Macaulay did far more than read and draw to create the 336-page book. He talked often with doctors and researchers and attended several surgeries to better learn what these body parts look like in real life. Macaulay even held a spleen in his hand!

What's a spleen? It's part of your infection-fighting lymphatic system, a small organ in the belly that also traps red blood cells when they're worn out. That's another example of how the body finds a way to solve problems, in Macaulay's view.

Red blood cells wear out, so they need somewhere to go. To the spleen! There, the spleen breaks them down, keeps iron and some amino acids. Then, the rest becomes bile pigment — coloring for the yellow-green digestive fluid called bile. For all the majesty of the human body, Macaulay found there's plenty of dirty work that needs to be done.

"Your body is an oxygen and nutrition highway system that also needs to carry garbage away," Macaulay said.

By describing your body as a highway system, Macaulay makes something very complicated easier to understand. He does the same thing when he dips into the human head. A cross-section of the head looks like a slice into the Earth with its layers, from crust to core. Down deep, there's theand white matter. Closer to the surface, there are layers of protective membrane and skull bone. Up top, your scalp spreads out like a farmer's field, sprouting hair instead of wheat.