I have ordered the compiled service record for John Falls (D K H), to determine whether John Salls is he. While I'm waiting for the additional information, I have not added data about John Salls elsewhere.
He was born in 1824/25. [source: date: 2 (36 in 1861)]
On 29 November 1861, he enlisted and was mustered into service, in company K, at Philadelphia, Pennsylvania. Captain Charles Brown (of the 91st) mustered him into service. [sources: 1, 2]
He is listed on the compay K muster-in roll, dated Philadelphia, Pennsylvania, 3 December 1861. [source: 4]
On 4 December 1861, he was transferred from company K to company H. [source: 2]
He is listed on the 31 December 1861 company K muster roll, as transferred to company H. [source: 2]
He is listed on the 10 September to 31 December 1861 company H muster roll. Whether he was present or absent isn't stated. He is not on any later muster rolls. [source: 1, 2]
1 index to compiled service records of volunteer Union soldiers who served in organizations from the state of Pennsylvania (John Salls)
2 compiled service record, K H 91 PA (John Salls)