As soon as casualties are ready for evacuation from the R.A.P. they are handed over to the Bearer Section of a Field Ambulance to be carried to their Advanced Dressing Station. As it is practically never possible to establish the Main Dressing Station sufficiently far forward to convey stretcher cases to it in one relay, and at the same time have it accessible to motor ambulances, light railways and other means of rapid evacuation, Advanced Dressing Stations are set up as near the front as can be evacuated to the Main Dressing Station by horsed ambulances with reasonable safety by day as well as by night. The evacuation of the wounded up to this point must usually be done at night on account of enemy observation; though the walking wounded are often able to take advantage of lulls in the hostile fire and make their way out during the day. Usually arrows are put up along the route pointing the direction for “walking wounded.” The Main Dressing Station of the Field Ambulance is provided with facilities for attending to cases requiring immediate operation as the only means of saving life. It must be remembered that this Unit is on the field of actual operations and within reach of the direct fire of the enemy. The sick and wounded are here sorted, classified and evacuated as soon as possible to the Casualty Clearing Station (C.C.S.). The few mild cases that can be returned to the line or sent to near-by rest camps after twenty-four or forty-eight hours are held at the Field Ambulance, it being necessary to conserve, as much as possible, the man-power for the line. The Casualty Clearing Station affords the next relief. This is the first Unit completely equipped for urgent, formal major operations, and some have X-ray apparatus and electrically-heated operating tables. Although cases are not carried to a finality of treatment, and are only kept until fit to move after relief is given, practically all wounds are dressed at the C.C.S. After emergent operations wounds are often packed with dressings and hurried on to a general hospital in the Lines of Communication. It must be remembered that these Units are within range of enemy guns and liable to get short notice from the enemy, by concentrated high explosive shell-fire, to vacate, or they may have to advance with the advance of their own troops. Constant action is therefore necessary to maintain rooms for the steady stream of wounded which they must always be prepared to handle. It is only the most urgent operations that are performed, such as wounds of the abdomen, chest and brain, or such wounds as are liable to become hopeless through infection or complications before reaching the base. The C.C.S. is usually located at a rail head and has access to ambulance trains for evacuation. These trains are wonderfully equipped with an emergency operating room, kitchen, dining room for up-patients and Staff sleeping berths, dispensary, medical officers, nurses and orderlies.