I do not know how long we slept, but when we awoke, we no longer felt tired, as we were the evening before. After waking, I noticed that the other two still sleeping, and I immediately began examing our surroundings. I than began thinking about how the captain of this submarine would provide us with air, as our supply of air in that room would not last much longer. Humans breathe in the air, but breathe out a gas that is poisonous to again breathe in. As the room's air supply was used, it filled with the poisonous gas we breathed out. If we had not received new supplies of air, we would soon have died from breathing in the poisonous gases. Although the room was quite large, we had already breathed in a great deal of the air supply during the night, and now the room was become filled with the poisonous gas we breathed out.