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Updated: June 3, 2025
In the animal of complicated structure special mechanisms are necessary that the essential oxygen be brought to the blood and the useless carbon dioxide removed. The respiratory organs or tract include the mouth, nose, larynx, trachea, bronchial tubes, and the lung-tissue proper or the air-cells.
The substance of the lungs consists of bronchial tubes, air-cells, blood-vessels, nerves, and cellular membrane. The bronchial tubes are merely continuations and subdivisions of the windpipe, and serve to convey the external air to the air-cells of the lungs. The air-cells constitute the chief part of the lungs, and are the termination of the smaller branches of the bronchial tubes.
The problem in baking, then, is the quick application of heat rather below than above the loaf, and its steady continuance till all the air-cells are thoroughly dried into permanent consistency. Every housewife must watch her own oven to know how this can be best accomplished.
This impure blood passes to the capillaries of the air-cells in the lungs, where it gives off carbonic acid, and, taking oxygen from the air, then returns to the left side of the heart, from whence it is sent out through the aorta and its myriad branching arteries to every part of the body.
The problem in baking, then, is the quick application of heat rather below than above the loaf, and its steady continuance till all the air-cells are thoroughly dried into permanent consistency. Every housewife must watch her own oven to know how this can be best accomplished.
Every person inspires air about twenty times each minute, using half a pint each time. At this rate, every pair of lungs vitiates one hogshead of air every hour. The membrane that lines the multitudinous air-cells of the lungs in which the capillaries are, should it be united in one sheet, would cover the floor of a room twelve feet square.
Then the land rose, and the elephant passed by the new tracts into the north. Its next representative, Tetrabelodon, is found in Asia and Europe, as well as North Africa. The frame is as large as that of a medium-sized elephant, and the increase of the air-cells at the back of the skull shows that an increased weight has to be sustained by the muscles of the neck.
After birth, the heart discharges the blood from its right ventricle into the lungs; and after passing through these it is emptied into the left ventricle: thus the heart opens the lungs. This it does through the pulmonary arteries and veins. The lungs have bronchial tubes which ramify, and at length end in air-cells, into which the lungs admit the air, and thus respire.
It breathes, but does so imperfectly, so that air does not enter all the smaller air-cells; and its voice is a whimper rather than a cry.
To make them a little nicer, a large spoonful of melted butter may be added, and two beaten eggs. This will require longer to rise, as butter clogs the air-cells, and makes the working of the yeast slower. The quantities given for bread will make two dozen muffins.
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