A 25-year-old man was admitted for pain and distention of the abdomen. He had a three-day history of dizziness, fatigue, myalgia, and mild fever. On physical examination, he was in shock, with ascites and oculofacial congestion. Bowel sounds were absent. A doughy mass in the right inferior fossa was palpable and slightly tender. The peripheral white-cell count was 16,000 cells per cubic millimeter (78 percent neutrophils), and the hematocrit was 40 percent. A radiograph obtained after the administration of a barium enema showed large edematous cecal folds (arrows, Panel A). The patient, a shepherd, was living in a remote, rural . . .