A note on the days between 2nd Bull Run and Sharpsburg:

The regiment was engaged in picket duty on the Leesburg Road and Little
River Turnpike where they arrested many stragglers from the disastrous
fields of 2nd Bull Run and Chantilly. On September 14, they set forth
toward Frederick, and on the 17th were ordered on to Sharpsburg, arriving
on the battlefield of Antietam at 9:00 am on the 18th after a forced march
of 23 miles. They took position in line and relieved troops exhausted from
the fight. After retiring to Camp near Sharpsburg on the 19th, they engaged
in picket duty along the Potomac. The weather was excessively hot and much
sickness prevailed. John got quite ill, himself. Disease was a terrible
problem during the Civil War; sanitary practices were virtually unheard of.
In this case, too, the thousands of putrifying bodies left after the Battle
of Antietam did nothing to help the situation. Burial details could not
work fast enough to prevent it.