
Doctors only attended 3 semesters of 13 weeks of medical school. Medical schools were all over during the Civil War period. Most of these were just diploma factories, providing very little real training. As there was no medical licensing board at this time, these diploma factories were tolerated. The good medical schools were at the established colleges, i.e. Princeton, Yale, etc. These schools' programs were only 1 year programs, although 2 years was recommended. The first year consisted of all book instruction, with just the last few weeks being residence-type training. The second year was just a repeat of the first year. If you didn't learn it the first time, they theorized, you'd get it on the second time through.
When the Minie Balls that were common during the war hit someone, bacteria were usually carried into the wound, making it worse. After an operation, they thought it good if pus formed. They called it "laudable pus," when really the pus was a sign of massive bacterial infection that would usually kill the soldier.
Embalming became a science during the Civil War, as many families wanted their dead relatives' body brought back from the war. There was a whole new profession built around embalming during the war. Families could hire an "embalming surgeon" to embalm the body of the dead soldier and bring it back for burial.
An important idea that came out of the war was that medical personnel were neutrals, and should not be fired on, taken prisoner, and captured like common soldiers.