"Just a minute," I said, "I remember now. I was not on my level--that was not my book store." "The card orders me to call up the hospital," said the guard. "It is unnecessary," I said. "Do not call them." The guard gazed first at me and then at the card. "It is signed by a Lieutenant and you are a Captain--" his brows knitted as he wrestled with the problem--"I do not know what to do. Does a Captain with an affected memory outrank a Lieutenant?" "He does," I solemnly assured him. Still a little puzzled, he returned the card, saluted and was gone. It had been a narrow escape. I got out my atlas and read again the rules that set forth my right to be at large in the city. Clearly I had a right to be found in the medical level--but in trying to buy a book there I had evidently erred most seriously. So I carefully memorized the list of shops set down in my identification folder and on my cards. For the next few days I lived alone in my apartment unmolested except by an occasional visit from Holknecht, the laboratory assistant, who knew nothing but chemistry, talked nothing but chemistry, and seemed dead to all human emotions and human curiosity. Applying myself diligently to the study of Armstadt's books and notes, I was delighted to find that the Germans, despite their great chemical progress, were ignorant of many things I knew. I saw that my knowledge discreetly used, might enable me to become a great man among them and so learn secrets that would be of immense value to the outer world, should I later contrive to escape from Berlin. By my discoveries of the German workings in the potash mines I had indeed opened a new road to Berlin. It was up to me by further discoveries to open a road out again, not only for my own escape, but perhaps also to find a way by which the World Armies might enter Berlin as the Greeks entered Troy. Vague ambitious dreams were these that filled and thrilled me, for I was young in years, and the romantic spirit of heroic adventure surged in my blood. These days of study were quite uneventful, except for a single illuminating incident; a further example of the super-efficiency of the Germans. I found the meals served me at my apartment rather less in quantity than my appetite craved. While there was a reasonable variety, the nutritive value was always the same to a point of scientific exactness, and I had seen no shops where extra food was available. After I had been in my apartment about a week, some one rang at the door. I opened it and a man called out the single word, "Weigher." Just behind him stood a platform scale on small wheels and with handles like a go-cart. The weigher stood, notebook in hand, waiting for me to act. I took the hint and stepped upon the scales. He read the weight and as he recorded it, remarked: "Three kilograms over."