Working Sketch by Sketch

So it was that long ago that Macaulay started work on the book. An architect by training, he said he started out at square one, knowing very little about what goes on inside the body. Macaulay got going by doing a lot of reading and research. And he did sketch after sketch to get the drawings right.

"I don't believe I understand something until I draw it," he said.

To explain how the body gets and distributes oxygen, Macaulay created "Ride of a Lifetime," taking oxygen molecules on a rollercoaster ride. They drop from the trees (thanks to photosynthesis) and then these very important passengers ride around the body in, getting dropped off everywhere they're needed.

In the book, Macaulay begins with your smallest body part — the super-tiny atoms in your tiny cells. Unseen unless you're looking through a powerful microscope, there's a whole world of activity going on in each of those cells. All that is you was built cell by cell, from the moment you existed. So how many cells is that? Oh, many trillions, Macaulay writes.

He closes the book by looking at the reproductive system — once again back to a single cell. This time, it's one cell that divides until there are just too many to count. In other words, a baby who will grow up to have trillions of cells.

Macaulay's research began with books like Gray's Anatomy, a famous and not-very-easy-to-read guide to the body. But he also took a long look at the Anatomy Coloring Book. In fact, he encourages kids to draw and color the parts of the body. It's a great way to learn what they look like and how they all fit together, he said.