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Updated: June 26, 2025
The improper performance of the functions of the skin seems to cause a peculiar sensitiveness of the air-tubes, and to render them liable to the occasional occurrence of that spasm which produces asthma.
The columnar epithelium consists of pear-shaped or elongated cells, frequently as a single layer of cells on the surface of a mucous membrane, as on the lining of the stomach and intestines, and the free surface of the windpipe and large air-tubes. The glandular or spheroidal epithelium is composed of round cells or such as become angular by mutual pressure.
"I clumped about for a while on the sandy bottom so as to get familiar with the air-tubes, signal-cords, and all that, and then I signalled to be hauled up a bit; and, after a good deal of trouble, I got on board the vessel which I was sure was a Spanish galleon. As I stood on her upper deck, looking around, I felt as if I was in a world of wonders.
When patients with severe inflammations of the lungs become too weak or too deeply narcotized to cough, then attacks of suffocation from the accumulation of mucus in the air-tubes are likely to occur at any time.
As a general rule, insect wings that are intended for employment in flight are transparent membranes, with the course of the air-tubes marked out upon them as opaque nervures. These air-tubes, it will be remembered, are lined by spires of dense cartilage; and hence it is that they become nervures so well adapted to act like tent-lines in keeping the expanded membranes stretched.
On this ground it is therefore needless for me again to enter, and I may pass at once to consider those ailments which rise in increasing importance from a simple cold or catarrh to inflammation of the air-tubes or bronchitis, inflammation of the lung substance, as pneumonia, and inflammation of the membrane which lines the chest and covers the lungs, or pleurisy.
The special arrangements of the vessels and the ducts of all the glands, of the air-tubes and vesicles of the lungs, of the parts which make up the skin and other membranes, all the details of those complex parenchymatous organs which had confounded investigation so long, have been lifted out of the invisible into the sight of all observers.
In the great majority of instances inflammation of the lung-substance does not go on to the last stage, and recovery is not only possible, but probable, from congestion and solidification of the organ. Pneumonia, too, usually attacks only a portion of one lung, while in bronchitis the air-tubes of both are always involved.
The special arrangements of the vessels and the ducts of all the glands, of the air-tubes and vesicles of the lungs, of the parts which make up the skin and other membranes, all the details of those complex parenchymatous organs which had confounded investigation so long, have been lifted out of the invisible into the sight of all observers.
Oxygen has been proved to be indispensable, and hence we see a reason for the luminous organs in the glow-worm being so intimately connected, as above mentioned, with the air-tubes that ramify through the insect. This fact of itself might be taken as a strong indication of the chemical nature of the process to which phosphorescence is due.
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