PHILADELPHIA — It was the fourth time Mike Abdullah was attending the class in basic combat medicine for civilians, and he still shook his head ruefully at the scenes playing out before him. An 11-year-old boy lay on the ground and tried his best to be limp, dead weight, while a former Navy medic taught those around him the best way to carry him to safety. A female nurse in scrubs showed a group of adults and children how to locate the brachial artery and stop massive bleeding with the pressure of a single thumb. One of her male counterparts...