2/8 DESIGN IN NATURE 



I am disposed to lay it down as an axiom that whenever jjale, unstriated, involuntary muscular fibres occur m 

 quantity, ajid especially when they assume the annular form, or when they are arranged at right angles and obliquely, 

 rhythmic movements are not only possible but probable. 



In order to produce a rhythmic movement all that is required is a series of muscular fibres — striated or non- 

 striated is immaterial — invested with the double power of shortening and elongating vitally. 



The respiratory movements of the higher animals are due to a twofold cause : namely, a -want on the part of 

 the system for oxygen, and a desire to get rid of carbonic acid, which is a poisonous, deleterious gas. 



The respiratory process is carried on in two ways : — 



(«) By means of the skin and mucous surfaces and tissues generally, and 



(b) By means of a respiratory apparatus which may take the form of gills or lungs. 



The respiratory movements have a wide range as regards frequency, intensity, and duration. Thus in hiber- 

 nating animals they are reduced to a minimum : the same thing happens in the condition known as trance. The 

 movements are less pronounced in the recumbent than in the sitting, and in the sitting than in the standing positions. 

 They are slower in walking than in running, and in asthma, due to paralysis or partial paralysis of the diaphragm, 

 they are violent ; persons so afflicted seizing the backs of chairs or tables to afford fixed points with a view to 

 relieving their breathing. 



Respiration is divided into costal and diaphragmatic according as the ribs or the diaphragm take the leading 

 part — the costal being most pronounced in man, the diaphragmatic in woman. There is reason to believe that 

 the use of corsets and tight clothing in modern woman emphasises the diaphragmatic respiration by enfeebhng and, 

 to a large extent, destroying the action of the thoracic and abdominal muscles, especially the latter. 



The Cheyne-Stokes respiration is a greatly enfeebled form of respiration due to fatty heart and other causes which 

 need not be considered here. 



The respiratory movements are spoken of as natural and forced according as they are calm or the opposite. 

 In calm breathing there are usually nine inspirations and nine expirations per minute. In calm as well as in forced 

 breathing not only the muscles of the diaphragm and chest but also those of the abdomen are brought into play. 

 In forced breathing the muscles of the neck, shoulder, root of humerus, back, pelvis, &c., are involved. The fact 

 that the respiratory movements vary greatly in different individuals at different times and under varying conditions 

 necessitates a certain amount of accommodating power in the muscular arrangements. 



In the early foital condition in man the respiratory system appears as an embranchment or diverticulum of 

 the alimentary system, and we may consider it as a large-branched, specially-modified gland lined with mucous 

 membrane and consisting of a conducting portion and a secreting portion. The hmgs being originally a diverticulum 

 from the alimentary canal, it is well not to lose sight of this connection when speaking of the rhythmic movements 

 of the lungs and intestine, and of similar movements occurring in the thorax and abdomen. It is not possible, 

 in my opinion, to separate the rhythmic movements occurring in the chest from those occurring in the abdomen. 



As a matter of fact, the thoracic and abdominal cavities open and close alternately ; the opening and enlarging 

 of the chest necessitating the closing or diminution of the abdomen and vice versd. This is especially the case in 

 forced respiration. The one movement cannot take place without the other : neither does the one movement cause 

 the other. 



The diaphragm by its alternate upward and downward movements plays an important part in the alternate 

 increase and decrease of the thoracic and abdominal cavities. When the diaphragm descends it increases the size 

 of the chest at the expense of the abdomen : when it ascends it increases the size of the abdomen at the expense of 

 the chest. 



The muscles of the chest and diaphragm shorten and close when those of the abdomen elongate and open, 

 and the converse. The thoracic and abdominal muscles are co-ordinated for the express purpose of alternately 

 opening and closing the thoracic and abdominal cavities. These cavities are opened and closed by vital muscular 

 movements assisted by the elasticity of the ribs, cartilages, and other structures engaged. 



The muscles of the thorax and abdomen are complemental co-ordinated muscles, and the one set closes or shortens 

 when the other set opens or elongates, and vice versd. The diaphragm is also a co-ordinated muscle. It is invested 

 with a double power— that is, it can close or shorten in all its diameters and become flat by a centripetal movement, 

 or It can open or elongate in all its diameters and become arched by a centrifugal movement. The chest, abdominal, 

 and diaphragmatic movements are vital in their nature ; the elasticity of the ribs and other structures performing 

 a useful but subordinate function. 



The chest, abdominal, and diaphragmatic movements are essentially rhythmic in character. The chest, as indi- 

 cated, may not inaptly be compared to the left auricle of the mammahan heart ; the abdomen to the left ventricle, 

 and the diaphragm to the auriculo-ventricular or mitral valve. 



