Captain Hugh D. Cameron, originally of the Alamutcha Infantry, was temporarily commanding the regiment on March 8, 1864. Cameron was a 17-year-old unmarried student when he enlisted in March, 1861.
Cameron was substituting for Major George LaValle Donald, who had commanded the regiment since the death of Colonel McElroy at Fort Sanders. Donald, an unmarried 23-year-old farmer when he joined the Secessionists as a lieutenant in 1861, was temporarily commanding the brigade in the absence of General Humphreys who presumably was on furlough.
In a letter to General Longstreet, reprinted by independent historian Jess N. McLean, Cameron said the 13th “has an aggregate present of 208” men, about the size of two companies at the start of the war.
13TH MISSISSIPPI INFANTRY REGIMENT 
You have to wonder [what] went through their minds when they looked around at muster and noticed there were so few men in the regiment. Were they courageously carrying on or deluded about the course of events? Or did they hope for a negotiated peace?
I imagine they were pretty close to despair, Ralph, but somehow they hung on.
A few more, perhaps as many as a dozen, likely were on furlough at this time, though there’s no confirming record as far as I know. But even though the regiment acquired some conscripts as the year went on, the casualties from the upcoming Overland Campaign would almost halve this total by mid-summer.