How “Gray’s Anatomy,” a book of drawings featuring blood vessels, muscles, the nervous system and other squeamish things, came to be one of the world’s most widely read books ...

When it came to late-19th century brain studies, things were complicated further by the nature of nervous tissue. Neurons were hard to see without special staining.

The nervous system was also well suited to the embryological method because as axons grow, they develop myelin sheaths—insulating layers of fat and protein—which repel the silver microcrystals ...