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Untitled Article
vision that this ejection of the blood should be made in the right direction ; to provide , for instance , that the contraction of the right ventricle should propel the blood into the pulmonary artery , and not back into the right auricle . This provision is made in the valves of the heart . Between each auricle and ventricle there is a valve . This valve consists of a fold of membrane , thin , but exceedingly firm and strong , placed around the opening . As long as the blood proceeds forward in the proper course of the circulation , it presses this membrane close to the side of the heart , and therefore and thereby prevents
it from occasioning any impediment to the onward current . But when , by the contraction that follows , the blood is pressed in all directions , and attempts to re-enter the auricle , it insinuates itself between the sides of the ventricle and the membranous valve , forces it up , and carries it over the mouth of the passage , and completely shuts up the channel . Were there not a further provision , the valve itself would be forced backwards into the auricle ; but this is prevented by means
of tendinous strings proceeding from muscular columns that line the inside of the ventricle , which strings are fastened to the loose edge of the valve . These tie it down , and prevent its going backwards too far . The contrivance is rendered still more perfect by vital action , which now comes into play . Muscle is excited to contraction by any stimulus ; by none more than by distension . Exactly in proportion
to the force with which the valve is pushed backwards , and so stretches the tendinous threads , and consequently distends the muscular column in which the tendinous threads end , do the muscular columns contract , and , by their contraction , force the valve to keep in its proper place . 4 Among the countless instances of wise and beneficent adjustment familiar to the student of nature , there is commonly some one upon
• which his mind rests with peculiar satisfaction , —some one to vrhich it constantly recurs , as affording the proof on which it reposes , of the operation of an intelligence that has foreseen and planned an end , and provided for its accomplishment by the most perfect means . And surely nothing is more worthy to become one such resting place to the philosophic mind , than the structure and action of the valves of the heart . An anatomist , who understood the structure of the heart ,
might say before he saw it in action , that it would play . But , from the complexity of its mechanism , and the delicacy of some of its parts , he would be apprehensive that it would be liable to constant derangement ; and that it would soon wear itself out . And yet does this wonderful machine go on night and day for eighty years together , at the rate of a hundred thousand strokes every twenty-four hours ;
having at every stroke a great resistance to overcome ; and it continues this action for this length of time , without ceasing and without wearines * . That it should continue this action for this length of time without disorder is wonderful ; that it should be capable of continuing it without weariness is still more amazing . Never for a single moment , night or day , does it intermit its labour , neither through our waking nor our sleeping hours . On it goes without intermlision , yet it never feels fatigue , it never needs rest , It is never conscious , of exhaustion . 4 What it it that renders it capable of thia incessant and untiring
Untitled Article
180 J > r . Southwood Smith on the Animal Economy ,
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Citation
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Monthly Repository (1806-1838) and Unitarian Chronicle (1832-1833), Feb. 2, 1833, page 130, in the Nineteenth-Century Serials Edition (2008; 2018) ncse.ac.uk/periodicals/mruc/issues/vm2-ncseproduct2608/page/62/
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