558. The parole and countersign are issued daily from the principal head-quarters of the command. The countersign is given to the sentinels and non-commissioned officers of guards; the parole to the commissioned officers of guards. The parole is usually the name of a general, the countersign that of a battle. 559. When the parole and countersign cannot be communicated daily to a post or detachment which ought to use the same as the main body, a series of words may be sent for some days in advance. 560. If the countersign is lost, or one of the guard deserts with it, the commander on the spot will substitute another, and report the case at once to the proper superior, that immediate notice may be given to head-quarters.