The People's Common Sense Medical Adviser in Plain English: or, Medicine Simplified, 54th ed., One Million, Six Hundred; and Fifty Thousand — John Stuart Mill — John Shaqi
The People's Common Sense Medical Adviser in Plain English: or, Medicine Simplified, 54th ed., One Million, Six Hundred; and Fifty Thousand
John Stuart Mill · en
Experiments have shown that the small arteries may be directly
influenced through the nervous system, which regulates their caliber by
controlling the state of contraction of their muscular walls. The effect
of this influence of the nervous system enables it to control the
circulation over certain areas; and, notwithstanding the force of the
heart and the state of the blood-vessels in general, to materially
modify the circulation in different spots. Blushing, which is simply a
local modification of the circulation, is effected in this way. Some
emotion takes possession of the mind, and the action of the nerves,
which ordinarily keep up a moderate contraction of the muscular coats of
the arteries, is lost, and the vessels relax and become distended with
arterial blood, which is a warm and bright red fluid; thereupon a
burning sensation is felt, and the skin grows red, the degree of the
blush depending upon the intensity of the emotion.
The pallor produced by fright and by extreme anxiety, is purely the
result of a local modification of the circulation, brought about by an
over-stimulation of the nerves which supply the small arteries, causing
them to contract, and to thus cut off more or less completely the supply
of blood.
* * * * *
CHAPTER VIII.
PHYSIOLOGICAL ANATOMY.
THE ORGANS OF RESPIRATION.
THE ORGANS OF RESPIRATION are the Trachea, or windpipe, the Bronchia,
formed by the subdivision of the trachea, and the Lungs, with their
air-cells. The _Trachea_ is a vertical tube situated between the lungs
below, and a short quadrangular cavity above, called the _larynx_, which
is part of the windpipe, and used for the purpose of modulating the
voice in speaking or singing. In the adult, the trachea, in its
unextended state, is from four and one-half to five inches in length,
about one inch in diameter, and, like the larynx, is more fully
developed in the male than in the female. It is a fibro-cartilaginous
structure, and is composed of flattened rings, or segments of circles.
It permits the free passage of air to and from the lungs.
The _Bronchia_ are two tubes, or branches, one proceeding from the
windpipe to each lung. Upon entering the lungs, they divide and
subdivide until, finally, they terminate in small cells, called the
_bronchial or air-cells,_ which are of a membranous character.
[Illustration: Fig. 43.
An ideal representation of the respiratory organs. _3._ The
larynx. _4._ The trachea. _5, 6._ The bronchia. _9, 9, 9, 9._ Air-cells.
_1, 1, 1, 2, 2, 2._ Outlines of the lungs.]