HEADQUARTERS DEPARTMENT OF THE MISSISSIPPI,
Saint Louis, March 28, 1862.

 Hon. E. M. STANTON,
Secretary of War, Washington :

SIR: I have directed that Jefferson Barracks be evacuated, the public property to be removed, and the buildings to be turned over to the medical department for a hospital. General Buell reports the number sick and absent of his army (of 101,000 men)to be 30,000, or nearly one in every three. This is certainly an enormous sick list for an army that has been engaged in no serious battle. Of the regiments which I have recently sent up the Tennessee River, now numbering in all about 50,000 men, all the sick were left behind in hospital, and yet, after being less than two weeks in the field, it is reported that 5,000 men are already on the sick list. This, at a healthy season of the year, is certainly an unprecedented condition of things, and would seem to indicate a radical deficiency somewhere. I am confident it does not result from a want of proper provisions and hospital stores, for no army was ever better supplied. I have given the subject as much attention as my time would permit, and I think one great source of the evil is in the incompetency of the brigade and regimental surgeons of volunteers. It is alleged that men are placed on the sick list and given certificates of inability as a mere matter of favoritism, in order that they may visit their homes or avoid disagreeable service in the field. On several occasions I have ordered medical boards to re-examine men sent from the field to the hospitals in this city, and a large portion of those so re-examined have been reported fit for duty in the field. This is a serious evil, but very difficult to remove. To order men into the field who are reported by their surgeons as sick would seem a cruel procedure on the part of a commander.

In detailing General Denver for the command in Kansas I followed the advice of the officers of General Hunter's staff. They gave it as their opinion that he was best suited for the place, and as I had very little personal acquaintance with him I felt bound to follow the best advice I could obtain. Subsequent information convinces me that it was good, and that a better selection could not have been made. There are few, if any, enemies in Kansas, and the qualities most required there are administrative; I think General Denver would preserve peace on the border and enable me to send most of the Kansas troops into the field, where they might be of some use. As it now is they are really worse than useless, for they compel me to keep troops from other States on the Missouri border to prevent these Kansas troops from committing murders and robberies. It appears, however, that there are some political influences connected with this matter. Not being a politician, this did not occur to me. I am a little surprised, however, that politicians in Congress should be permitted to dictate the selection of officers for particular duties in this department. Under such circumstances I cannot be responsible for the results. Nevertheless I shall comply with the President's wishes, and place some other officer in command in Kansas as soon as I can spare one for that purpose.

On consultation with Major Donaldson, just from New Mexico, it has been determined to send out an expedition of one regiment of cavalry, three of infantry, and two or three batteries. He does not deem a larger force necessary. Moreover it will be a very difficult task to get this number through at this season, as there is no forage or grass on the road. Many say that all our animals will die for want of food before they can reach Fort Union, while others say they can get through if managed with care. The urgency of the case requires, in my opinion, that we run all risks in order to save General Canby's command if it is possible. It is estimated that each regiment will require at least 100 wagons to carry it through, and as there is no large amount of stores at Fort Union, the general supply train must follow as early as possible. I shall do everything in my power to urge the expedition forward as rapidly as possible.

Very respectfully, your obedient servant,

 H. W. HALLECK,

 Major-General.