A sentinel on the line of observation should always have the following instructions: The names of villages, streams, and prominent features in sight and where the roads lead. The number (if any) of his post, and the number of his and of the adjoining outguards; the position of the support; the line of retreat to be followed if the outguard is compelled to fall back; the position of advance detachments and whether friendly patrols are operating in front; to watch to the front and flanks without intermission and devote special attention to unusual or suspicious occurrences; if he sees indications of the enemy, to at once notify his immediate superior; in case of imminent danger, or when an attack is made, to give the alarm by firing rapidly; by day to pass in or out officers, noncommissioned officers, and detachments recognized as part of the outposts, and officers known to have authority to do so; to detain all others and notify the outguard commander; at night, when persons approach his post, to come to a ready, halt them, and notify the outguard commander; the latter challenges, ascertains their identity, and acts accordingly. When individuals fail to halt, or otherwise disobey, to fire upon them after a second warning, or sooner if they attempt to attack or escape; to require deserters to lay down their arms, and remain until a patrol is sent out to bring them in; to order deserters pursued by the enemy to drop their arms and to give an alarm; if they fail to obey they are fired upon; to require bearers of flags of truce and their escorts to halt and to face outward; to permit them to hold no conversation and to see that they are then blindfolded and disposed of in accordance with instructions from the support commander; if they fail to obey to fire upon them; at night, to remain practically stationary, moving about for purposes of observation only; not to sit or lie down unless authorized to do so; in the daytime, to make use of natural or artificial cover and assume such positions as to give him the best field of view; to inform passing patrols of what he has seen; to carry his weapon habitually loaded and locked and at will.