The information I previously passed on was obtained from subscription services which contain records from the Compiled Service Records developed by the War Department circa 1900 and maintained at the National Archives in Washington, DC and state records at state archives.
To obtain his full records you need to obtain his CSR files. One service is provided by this Message Board.
His records are found on microfilm, Microform M323, Roll 27.
You will however, be able to verify his unit ID through the National Park Service (NPS) Soldiers and Sailors System if you go to:
There you will be able to locate your man through either a search of his name or by unit ID
Here is what you will find therein. No more.
D. Marquis C. Christopher (First_Last)
Regiment Name 4 Texas Cavalry
Soldier's Rank_In Private
Soldier's Rank_Out Private
Alternate Name Demarquis C./Christopher