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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
Particles of the blood have also been observed to leave the stream , and to mingle with the tissues , and particles of the tissues to move into the stream , and to be carried away by it . Nerves follow the course of the arteries through all their ramifications , but it is for the capillaries that the great bulk of them are reserved ; innumerable nervous filaments are spread out upon them , and exert an important influence over their action .
The structure of the veins is different from that of the arteries . They have only two coats , being destitute of the fibrous coat ; they are also more numerous , and of greater capacity . The main power that moves the current of the blood through all
these vessels is evidently the contraction of the left ventricle of the heart . It is assisted in the arteries by their elasticity and by their contractile power . The trunk of an artery is always full to distension , and every fresh wave of blood that is thrown into it brings both its actions into play , which actions , alternately renewing and ceasing , cause the motion that is felt when the finger is pressed upon an artery , and constitute the pulse . * The state of the pulse indicates , as you know , the state of the
circulation . The state of the circulation is closely connected , not only with the vital state , but with the vital action of almost every organ of the body . The circulation is the great centre of the organic life . A certain state of the organic life is always coincident with a certain state of the circulation . The pulse is the index of this state . Physicians endowed with the power of observation , and gifted with tactile
discernment , who have been placed in situations affording them large experience , have sometimes acquired an astonishing skill in judging of the morbid condition of the system from the state of the pulse . It is universally admitted to be an invaluable guide in inflammation . It is equally so in fever . It will often tell with great certainty , to those who have studied it , when the abstraction of blood will be beneficial ; when , on the contrary , wine should be given , or when nothing should be done : and this is the more important because the great skill in managing a case of fever consists eminently in knowing these three
points . ' It used to be thought that the capillaries had a propelling power of their own , but recent experiments have proved that they have it not , but that the blood circulates through them in consequence of the impulse of the heart ' s contractions ; and as after death the action of a syringe can propel a fluid into the extreme capillaries with ease , it is not difficult to believe that a force equal to sixty pounds can do it . The case is the same with the veins ; . the action of the heart
urges on the current through them also . The same tension does not exist in them as in the arteries , because there is a ready escape for the blood through the right auricle , but it rushes through them with equal force , and it is assisted by two auxiliary powers—by valves with which in many parts of the body the veins are furnished , and by the action
of a vacuum formed in the right auricle every time it dilates , which makes the blood hurry forward to fill up the void as soon as it cornea within its influence ; while the effect of the valves is to divide a long and heavy column of blood into several shorter ones , offering lews resistance .
Untitled Article
Dr . Southwood Smith on the Animal Economy . 199
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Citation
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Monthly Repository (1806-1838) and Unitarian Chronicle (1832-1833), March 2, 1833, page 199, in the Nineteenth-Century Serials Edition (2008; 2018) ncse.ac.uk/periodicals/mruc/issues/vm2-ncseproduct2610/page/55/
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