Because the human nervous system can stand only a certain amount of abuse battalions can be kept in the line only a certain length of time, which depends upon the activity upon that front, upon the exposure of the lines to the enemy, and so the extra nervous strain, or sometimes upon the urgency of advance or retreat. A relief may be very welcome, or very unwelcome, depending upon the same things, but also to a certain extent upon the quality of the dugouts in the lines, and the kind of accommodation outside. For, strange to say, the dugouts in the lines may be preferable, even with their added danger, because, on arriving at your rest station, your battalion may find, instead of the good billets they hoped for, a few forlorn-looking one-inch board huts, with only one-half the required accommodation, the temperature below freezing, and no stoves; or you may find only tents; or you may find virgin forest in which you are to build your own camp, while the rain comes down with monotonous persistence. It is midnight in the late winter, and the adjutant, Major P----, and I are just leaving H.Q. dugout on our way to reserve billets. The trenches are very dark, the light from the stars overhead not reaching to their depths. We throw down a glare from a flashlight, and a Tommy's voice angrily cries: "'Ave a 'eart there, myte; d'ye think ye're the only man in the army? Douse the glim." So we douse it, and decide that the best way to keep peace in the army is to pick our way along. Gradually our eyes become accustomed to the dark, and instinctively our feet keep on the trench mats as we twist and turn along the trenches. An occasional flare or star shell from the front lines aids us for a moment, but plunges us into deeper darkness afterwards. Our feet slip on the semi-frozen mud of the mats, over our heads in both directions shells sing at intervals, and we hear the pounding of the guns and bursting shells before and behind us. In the quieter moments we can hear a quarter of a mile away the rattle of transport wagons on the hard road as they bring their nightly loads of ammunition and food to the dump where we are going and where we expect to find our horses. We arrive at the dump, and here one might think he was in the midst of a large city market just before the dawn. Limbers, general service wagons, pack mules and men make a jumble of hurrying, scurrying workers. No lights dare be shown for fear of drawing the shells of the Germans, who have the range of this dump and have been shelling it during the day. Someone tells us our horses are just around a bend in the road, and we make our way there, and find the grooms holding the animals, which have become cold and restive with waiting.