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Untitled Article
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Note: This text has been automatically extracted via Optical Character Recognition (OCR) software. The text has not been manually corrected and should not be relied on to be an accurate representation of the item.
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Untitled Article
condor , eagle , hawk ,, Sec , are so constructed . We have examined the skeleton of the eagle , and found , as Macartney and other naturalists have described , the humerus , clavicle , scapula , sternum , vertebrae , femur , hollowed for the admission of air which is obviousl y in accordance with their powers of flight . In gallinaceous birds , however , the humerus is the only bone into which air is introduced . In the owl , again , the femur is filled with marrow , while in birds that run and command much power of the leg , as the ostrich , the femur is hollow and filled with air . True it is
that muscular power and activity always demand a high degree of oxygenation of the blood , in order that the muscular fibre shall receive a necessary and corresponding stimulus , but it b y
no means follows that this increase in the intensity of the function cannot be adequately effected by the lungs . It is well enough understood that the blood having been distributed from the left side of the heart to the extremities of the body loses its nutritient
and stimulating qualities , and is in that state returned to the right side of the heart . Here it arrives unfit for renewed circulation ; therefore , in order that its healthful qualities shall be restored , it is propelled into the lungs , where coming into contact , through the very thin parietes of the vessels , with the air which
during inspiration is admitted into the air-tubes and cells of that organ , it receives a fresh supply of oxygen , and is rendered again fit for circulation through the body . According to this viewwhich , since the days of Harvey , has been admitted ., with the
exception of a very few heretical authorities , among whom is Dr . Ker , of Aberdeen , who not very long ago puhlished a memoir denying the Harveian doctrines—the office of oxygenating" the blood is concentrated in the lungs of all warm-blooded animals . Why , therefore , should we imagine that in birds this fluid is returned from the lungs to the left side of the heart insufficiently arterialized ? and that it requires , therefore , to undergo a further
oxygenation in the course of its circulation through the body / The facility with which birds respire ; their performing this function without i ( painful fatigue ' or " punting , " can scarcely be adduced as an evidence in favour of the theory , because , as Macartney has shown , this seems to arise from the shortness and greater capacity of the air-tubes , which directl y communicate with the air-cells . The lungs , too , are so constructed as not to admit of any change
m their dimensions , being formed of a very compact tissue , and so closel y braced to the ribs and chest by a reflected dense membrane ( the . pleura ) as to preclude nil motion . The greater rapidity ol the circulation of the blood through the system , and the enlarged area of the air-cells of the lungs , in a great measure accounts for the blood of birds being" more hig hl y oxygenated than that ol mammalia . What , then , it may be asked , is the use of the air-cells which are so freel y distributed under the skin , between the
Untitled Article
274 The Study of Birds .
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Citation
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Monthly Repository (1806-1838) and Unitarian Chronicle (1832-1833), April 2, 1835, page 274, in the Nineteenth-Century Serials Edition (2008; 2018) ncse.ac.uk/periodicals/mruc/issues/vm2-ncseproduct2644/page/50/
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