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2/8 DESIGN IN NATURE<br />
I am disposed to lay it down as an axiom that whenever jjale, unstriated, involuntary muscular fibres occur m<br />
quantity, ajid especially when they assume the annular form, or when they are arranged at right angles and obliquely,<br />
rhythmic movements are not only possible but probable.<br />
In order to produce a rhythmic movement all that is required is a series of muscular fibres—striated or non-<br />
striated is immaterial—invested with the double power of shortening and elongating vitally.<br />
The respiratory movements of the higher animals are due to a twofold cause : namely, a -want on the part of<br />
the system for oxygen, and a desire to get rid of carbonic acid, which is a poisonous, deleterious gas.<br />
The respiratory process is carried on in two ways :<br />
(«) By means of the skin and mucous surfaces and tissues generally, and<br />
(b) By means of a respiratory apparatus which may take the form of gills or lungs.<br />
The respiratory movements have a wide range as regards frequency, intensity, and duration. Thus in hiber-<br />
nating animals they are reduced to a minimum :<br />
the<br />
same thing happens in the condition known as trance. The<br />
movements are less pronounced in the recumbent than in the sitting, and in the sitting than in the standing positions.<br />
They are slower in walking than in running, and in asthma, due to paralysis or partial paralysis of the diaphragm,<br />
they are violent ; persons so afflicted seizing the backs of chairs or tables to afford fixed points with a view to<br />
relieving their breathing.<br />
Respiration is divided into costal and diaphragmatic according as the ribs or the diaphragm take the leading<br />
part—the costal being most pronounced in man, the diaphragmatic in woman. There is reason to believe that<br />
the use of corsets and tight clothing in modern woman emphasises the diaphragmatic respiration by enfeebhng and,<br />
to a large extent, destroying the action of the thoracic and abdominal muscles, especially the latter.<br />
The Cheyne-Stokes respiration is a greatly enfeebled form of respiration due to fatty heart and other causes which<br />
need not be considered here.<br />
The respiratory movements are spoken of as natural and forced according as they are calm or the opposite.<br />
In calm breathing there are usually nine inspirations and nine expirations per minute. In calm as well as in forced<br />
breathing not only the muscles of the diaphragm and chest but also those of the abdomen are brought into play.<br />
In forced breathing the muscles of the neck, shoulder, root of humerus, back, pelvis, &c., are involved. The fact<br />
that the respiratory movements vary greatly in different individuals at different times and under varying conditions<br />
necessitates a certain amount of accommodating power in the muscular arrangements.<br />
In the early foital condition in man the respiratory system appears as an embranchment or diverticulum of<br />
the alimentary system, and we may consider it as a large-branched, specially-modified gland lined with mucous<br />
membrane and consisting of a conducting portion and a secreting portion. The hmgs being originally a diverticulum<br />
from the alimentary canal, it is well not to lose sight of this connection when speaking of the rhythmic movements<br />
of the lungs and intestine, and of similar movements occurring in the thorax and abdomen. It is not possible,<br />
in my opinion, to separate the rhythmic movements occurring in the chest from those occurring in the abdomen.<br />
As a matter of fact, the thoracic and abdominal cavities open and close alternately ; the opening and enlarging<br />
of the chest necessitating the closing or diminution of the abdomen and vice versd. This is especially the case in<br />
forced respiration. The one movement cannot take place without the other : neither does the one movement cause<br />
the other.<br />
The diaphragm by its alternate upward and downward movements plays an important part in the alternate<br />
increase and decrease of the thoracic and abdominal cavities. When the diaphragm descends it increases the size<br />
of the chest at the expense of the abdomen :<br />
the chest.<br />
when it ascends it increases the size of the abdomen at the expense of<br />
The muscles of the chest and diaphragm shorten and close when those of the abdomen elongate and open,<br />
and the converse. The thoracic and abdominal muscles are co-ordinated for the express purpose of alternately<br />
opening and closing the thoracic and abdominal cavities. These cavities are opened and closed by vital muscular<br />
movements assisted by the elasticity of the ribs, cartilages, and other structures engaged.<br />
The muscles of the thorax and abdomen are complemental co-ordinated muscles, and the one set closes or shortens<br />
when the other set opens or elongates, and vice versd. The diaphragm is also a co-ordinated muscle. It is invested<br />
with a double power—that is, it can close or shorten in all its diameters and become flat by a centripetal movement,<br />
or It can open or elongate in all its diameters and become arched by a centrifugal movement. The chest, abdominal,<br />
and diaphragmatic movements are vital in their nature ; the elasticity of the ribs and other structures performing<br />
a useful but subordinate function.<br />
The chest, abdominal, and diaphragmatic movements are essentially rhythmic in character. The chest, as indi-<br />
cated, may not inaptly be compared to the left auricle of the mammahan heart ; the abdomen to the left ventricle,<br />
and the diaphragm to the auriculo-ventricular or mitral valve.