Surely someone in the history of football had thought to look for dementia pugilistica. Unlike boxers, football players wear helmets, but a helmet can’t fully protect the head from damaging impact. The brain is suspended in a kind of thick jelly inside the skull, and a helmet can’t keep it from sloshing around. If you hit your head hard enough, the brain goes bashing against the walls of the skull.

Omalu had seen plenty of cases of brains destroyed within helmets. Omalu picked up Webster’s brain, carried it slowly to the cutting board, and turned it upside down and on its side and then over again. It was not at all what he expected. Regular folds of gray matter. No mush. No obvious contusions, like you find in dementia pugilistica. No shrinkage like you would see in Alzheimer’s disease. He reviewed the CT and MRI scans. All normal.

* * *

In his medical writings, Hippocrates mentioned what he called commotio cerebri—the loss of speech, hearing, and sight that could result from “commotion of the brain,” a vigorous shake or blow to the head.

The 10th-century Persian physician Abu Bakr Muhammad ibn Zakariya Razi is thought to be the first to make the distinction between the dramatic kind of brain injury— bruising and swelling and bleeding—that outright killed a person, and another, more subtle kind: an injury to the head that could make you dizzy, could even knock you unconscious, but from which you recovered. Razi was the first to use the term “cerebral concussion.”

In the early 16th century the Italian physician Jacopo Berengario da Carpi, a pioneer in the science of anatomy, came up with the idea that perhaps “brain commotion” was caused by the thrust of the soft structure of the brain against the solid case of the skull. The brain, he posited, was essentially bruised inside the skull by banging against its walls.

That would turn out to be a prescient theory. But there was little hope of advancing it, even when the microscope was invented at the end of the 16th century. Few people died from concussions, and so doctors didn’t routinely have concussed brains to autopsy. Without the underlying pathology to describe it, the word “concussion” remained a description, not a diagnosis. Most of the medical literature of the day pointed to good news: Unlike more severe forms of head injury, like crushing your skull or getting a bullet through your brain, this condition seemed temporary.

* * *

Mike Webster’s brain sat for two weeks in a white plastic bucket of formaldehyde at the morgue. When it was firm enough, Omalu pulled it out and put took a scalpel to the frontal lobe, cutting a section from it about the width of a stick of gum. He did the same to the parietal, occipital, and temporal lobes. He took the four slices to the lab at the University of Pittsburgh, where he had just finished his neuropathology training and knew the technicians and their particular expertise. He said nothing about whose brain he was giving them.