Princeton Battlefield State Park

Wounds [from battle] were first cleansed with lint, either dry or wet with oil, and bandaged lightly. Later they were to be washed with a digestive — a substance used to draw pus — and then covered with a bread-and-milk poultice, with oil for moisture. For the first twelve days, a cooling regiment of medicines and diet was recommended, on the theory that this lowered the danger of infection. The empiricists among the medical men of the time had noticed that a man ran a fever with an infection, and concluded, with somewhat superficial logic, that keeping him cool would lower the chances of the infection taking root.

Unfortunately, there was little or no interest in using clean bandages or instruments.