The human body is mostly water, and for days Dr. Brantly lay helpless in his bedroom as his fluids escaped faster than they could be replenished.

On a Monday morning, he said, he had three or four bouts of black watery diarrhea over 15 minutes, a sign of bleeding in his gastrointestinal system. The following morning, his vomit, a dark maroon, signaled more internal bleeding. He grew increasingly dehydrated despite receiving as many as eight liters of IV fluid a day. His diarrhea was frequent, and he had trouble breathing.

Lying in his bedroom, Dr. Brantly listened to music with words of Scripture. He spoke with his wife via FaceTime, and watched slideshows of his family.

Much of the time, he said, he felt alone. The medical staff caring for him had many other patients. “Sometimes I would fall asleep and I’d wake up and the person who had been there would be gone,” he said.