That was why, instead of immersing themselves in studious solitude, rehearsing their speeches, they spent the time in playing a game like a couple of schoolboys out for a holiday, with a good tea and a rest to follow. It is a dozen years since that happened, but those two men, who are among the hardest public workers of the day, are as fresh and fit for their duties now as they were then. And this, not from any natural strength or stamina, but simply because they have always taken pains to carry out the fundamental laws of health. The remainder of this book will be directed to the consideration of these laws, on which the whole question of breakdowns and their prevention depends. CHAPTER VI. THE HUMAN ENGINE AND HOW TO STOKE IT. An express train was standing in a London terminus, on the point of starting for her run to Edinburgh. Several persons were admiring the great locomotive, which was throbbing like a hound in leash, ready to be off the moment the guard’s signal was given. The guard waved his flag, and the train glided out of the station so smoothly, that the unwary passenger standing up in his compartment at the time was not even jolted. The first stopping-place, a hundred miles away, was reached on the stroke of time, without a hitch of any sort. The man who was responsible for this perfect running was not the driver so much as the stoker, that humble individual, as we are apt to regard him, whose duty it was to put the coal on the fires. Unless he had done his work efficiently, the best driver of the finest locomotive ever built could not have made a good run. He took care to use the right sort of coal, to put in enough of it to keep the fires bright, but not so much as to choke them up, and to shovel it in with discretion and at suitable times. Few people realise that there is a distinct art in stoking a furnace. Yet that stoker was not a happy man. He was sallow and of a livery type. He often suffered from headaches and spots before his eyes, heartburn and nausea. Although he was muscular and powerfully built, he frequently felt so tired and listless that he was hardly able to face his day’s work. All this was due to the circumstance that, although he had mastered the stoking of an engine, he had never learned to feed himself properly. He had not realised that he himself was an engine, quite as much so as the locomotive he worked on, and that the food he took was the fuel which supplied the driving power to his system and kept his machinery running. It had never dawned on him that there is an art in eating just as important as that of stoking, and demanding as much care and foresight.