Follow the course of the long procession of motor trucks which feed the army and you arrive at one of the great supply depots which every day send out the precise quota of supplies that are needed, with every motor truck having its schedule and keeping that schedule with the accuracy of a first-class passenger train. Follow the ambulances back from station to station, where the wounded men are examined to see if they are suffering from a hemorrhage and whether they are able to stand the farther journey and do not need an immediate operation, and you are brought to the immense base hospitals in a closely guarded and well ordered camp where every sanitary tradition known to modern life is absolutely enforced. One of these hospitals had twelve thousand beds and in the offensive of September 25, 1915, it discharged seven thousand patients in a day. Soldiers are restricted to the neighborhood of their billets and officers themselves must have passes if they travel outside the region occupied by their battalions. Everyone is a policeman under an intricate system guarding every detail of army secrets from any spy and from those gallant aviators who risk antiaircraft gunfire in the hope of bringing home some information to their side. Never has the Intelligence Service of an army had so many secrets to guard; never has it required such complicated measures of protection against espionage. In Napoleonic times, it was enough to know that your adversary was marching a hundred thousand men along parallel roads. This your cavalry scouts might discover; or a spy who had crossed the frontier in an unfrequented place might be watching the enemy's army and counting his numbers as they passed. Now the frontier is an intact line of trenches. The spies of Richelieu's day have been surpassed in this, our day--with their stories yet to be told. Many a man who spoke the enemy's language well has put on the enemy's uniform, joined one of his scouting parties between the trenches in the darkness, entered the enemy's trenches, heard all the talk and slipped back to his own lines safely. If apprehended, his fate was certain--death. The most efficient spy, of course, is the one with military training He knows the value of what he sees. Usually he is an officer of good family who has been cashiered for gambling or debt and takes a desperate chance out of patriotism and the hope of atonement. Naturally, the easiest route for spies was through Holland and Switzerland which became the gateway of passing spies and the playground of espionage and counterespionage. Gradually the restrictions tightened for all neutral travelers from capital to capital, while none were permitted to go into the zones of the armies, some twenty or thirty miles from the trenches.