Anna - It turns out that Maj. John M. Wall is a part of an interesting story involving men from Illinois (of Southern heritage) joining the Confederate Army. A book has been published about this group of men, and includes the story of how Dr. John M. Wall of Graves County, Kentucky, was recruited into this group as the men traveled south to enlist. It also details how Wall eventually took command of the regiment (actually a consolidated regiment - 15th/37th Tenn), and how he died from wounds suffered at the Battle of Atlanta. The whole book is not on line, but portions can be seen here:
https://books.google.com/books?isbn=1878208896