The first passenger railroad in the United States—the Baltimore and Ohio Railroad—began construction in 1828. Five years later, in 1833, the country saw its first fatal train accident. As train travel proliferated, train wrecks became “a surprisingly frequent form of disaster,†the historian Richard Selcer writes . And “the single worst type of railroad accident … not to mention the most frequent, was the rear-end collision.†Passengers involved in these train crashes would sometimes come down with a peculiar constellation of symptoms, including back pain, arm pain, headaches, hearing problems, anxiety, insomnia, lowered sex drive, and memory problems. These symptoms would appear even in the absence of any visible injuries. The condition was known colloquially as “railway spine.†The physician John Eric Erichsen suggested that it might be caused by the “‘jarring back and forth’ of the spine, although he could not explain what exactly happened to the spinal cord a...