"Yes, of course; he sets the stoker to firing up under the boiler. But what has that to do with getting tired and getting rested again? I don't see the connection."
"Yet it is clear enough," the Doctor responded. "The human system is a machine. It must have energy or force or whatever you choose to call it, to enable it to do its work. Now an engine gets its energy from the coal or wood burned under its boiler. This human machine derives its energy solely from food put into the stomach. When you are tired it means simply that your supply of physical force has run low. When you eat you replenish the supply, just as firing up does it for the engine."
"But Doctor," said Jack with an accent of puzzled inquiry, "how about those people that are always tired—'born tired' as they say? They eat, but they never get over being tired."
"Dyspeptics, every one of them," replied the Doctor. "It doesn't help an engine to shovel coal into its furnace if the coal doesn't burn. In the same way it doesn't strengthen a man to eat unless he digests and assimilates his food."
"Well now, if you people have sufficiently assimilated your food and your ideas," broke in little Tom, "let's get to work."
Some of the boys pulled the grass and piled it in rude shocks. The others carried it to the hut and bestowed it in one corner, ready for use. As they carried on the work the moon slowly went out, and just as they were finishing it, Jim Chenowith called out:
"There's the snow," and very gently the flakes began descending. "Jack you're a good weather prophet, and this time it's lucky for us that you are. Otherwise we should have had wet broom straw to sleep on all winter. By the way, how are we going to arrange our beds?"
"Why, we'll build a platform of small poles along the eastern wall of our house—the fireplace being on the western side. We'll divide this platform into compartments, each to serve as a bed. We'll lay clapboards on the poles to make a smooth surface, and on them we'll pile all the broom straw we've got. Then we'll wrap ourselves in our blankets and crawl in. Do you see?"
"Yes, but how about the fellows that must sleep under the Doctor's muslin window?" asked Harry. "Won't they sleep pretty cold, Doctor?"
"I don't think so," answered the Doctor. "The windows will keep out the cold quite as well as the logs themselves do."