The woman, grievously wounded in the mass shooting at a Walmart, lay on an operating table at the University Medical Center of El Paso as the chief of surgery, Dr. Alan Tyroch , turned her to clean the exit wounds. He knew what to expect, but it was still a horrific sight. She had two gaping holes the size of a man’s fist in her side and a third the size of a silver dollar where bullets had burst from her body.

Those bullets had also shredded her intestine. Dr. Tyroch hooked her up to a colostomy bag and a feeding tube. And he reached into another wound to pull out a bullet lodged in her shinbone. It had been flattened by its violent impact into a disc the size of a quarter.

The tragedy in El Paso on Saturday, carried out by a gunman armed with an AK-47-style rifle, and another deadly massacre on Sunday in Dayton, Ohio, in which the gunman used an AR-15-style pistol modified to act as a rifle, can be measured in death tolls — 22 in El Paso and nine in Dayton. But the damage done by such weapons is witnessed most clearly by members of the medical staff who care for the wounded.

The story of their lifesaving labors at the El Paso hospital, the only one in a 270-mile radius prepared to treat complex trauma patients, is one of heroics in the face of violence, and of the doctors and nurses, who, once the adrenaline rush died down, struggled to live with the horror of what they had experienced.