Practice of medicine was just emerging from the heroic era. There was no knowledge of the germ theory or antiseptic practices. These discoveries were many years away. More than 60 medical schools existed on America before the war and apprenticeships were common. Usual course of study for medical school was two terms of six-month lectures. During the time of the war large amounts of medical personnel were needed, therefore the educational requirements were not very extensive.
Not so much knowledge:
During the Civil War the knowledge, experience and training of physicians was very well regulated or checked up upon. The Union army had 98 doctors and the Confederacy only had 24! Considering this both armies were willing to take any person who claimed to have the sufficient medical experience to be a physician. Most of these Doctors carried around a surgeons guide manual and seemed to just follow the directions when performing life saving surgeries.(1)
Infection during the Civil War Era was a huge issue and medical personnel had little to no knowledge on the subject. They even believed that pus was a sign of healing so they would transfer pus from one patient to another, which in turn would just cause more infection! Doctors did not understand germs and how they were carried and spread. Due to this they violated almost every single rule of sterilization that is used today.(5)