Thomas Aumack Most Likely Was Discharged from Service Because of Diarrhea

I came across this list of soldiers in the 87th New York Infantry at the dmna.ny.gov site.

THOMAS B. AUMACK

Age, 18 years.

Enlisted at Brooklyn to serve three years.

Mustered in as a private in Co. C, November 5, 1861.

Discharged for chronic diarrhoea, September 23, 1862, at Fort Monroe, Virginia.

This seems to be the best account of why Thomas Aumack was not with the 87th or 40th New York Infantry regiments at the Battle of Antietam.  He probably had contracted the diarrhea in August or early September which ended his Army career.

--Old Secesh