Now came Tom's chance to serve the good cause. He was a proud boy, a few nights later, when he was permitted to go down to the kitchen with the Colonel and the Major, in order that he might creep into the hole they had made and enlarge it. His heels wiggled in the air. He laid upon his stomach in the upper part of the reversed "S" and plied the old knife as vigorously as it could be plied without making a tell-tale noise. When he had widened the passage, one of the men took his place in it and drove it downward. One night Colonel Rose in his eagerness got into the opening before the lower part of it had been sufficiently enlarged and stuck there. It was only by a terrible effort that Hamilton and Tom finally dragged him out, bruised, bleeding and gasping for breath. Finally, after many nights, Rat Hell was reached. A bit of rope, stolen from about a box of food sent a prisoner, had been made into a rope ladder. It was hung from the edge of the hole. The three crept cautiously down to Rat Hell. This haven did not seem much like heaven. With squeals of wrath, the rats attacked the intruders and the intruders fled up their ladder. They were no match for a myriad rats. Moreover they feared lest the noise would bring into the basement the sentry whose steps they could hear on the sidewalk outside. So they fled, taking their rope-ladder with them, and again, as ever, they replaced the bricks and painted them with the friendly soot. The next night, armed this time with sticks of wood, they fought it out with the rats and made them understand their masters had come to stay. Fortunately the fight was short. It was noisy and the sentry came. But when he opened the door from the street and looked into the darkness of the basement, the Union officers were safely hid under the straw and only a few of the defeated rats still squealed. At last the tunnel to the sewer could be begun. Colonel Rose had long since decided, by forbidden, stealthy glances from an upper window, just where it was to be. The measurement made above was now made below, the straw against the eastern wall was rolled aside and the old knife, or what was left of it after its battle with brick and stone, was put to the easier task of digging dirt. [Illustration: FIGHTING THE RATS From "Famous Adventures of the Civil War." The Century Co.] Soon a new difficulty had to be met. Before the tunnel was five feet long, the air in it became so foul that candles went out in it. So would the lives of the diggers have gone out if they had stayed in it long. Five of the fifteen now went down each night, so that everybody had two nights' rest out of three. But the progress made was pitifully slow. Man after man was hauled by his heels out of the poisonous pit, almost at his last gasp. Once, when Hamilton had been brought out and was being fanned back to life by Colonel Rose and Tom, the boy whispered: "Why not fan air into the tunnel?"