On the sounds caused by the circulation of the blood : being a thesis read in the University of Dublin for the degree of M.D., at the winter commencement, 1860 / by Arthur Leared.

  • Arthur Leared
Date:
1861
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Licence: Public Domain Mark

Credit: On the sounds caused by the circulation of the blood : being a thesis read in the University of Dublin for the degree of M.D., at the winter commencement, 1860 / by Arthur Leared. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    would only increase the sound; whereas its effect in small quantity is to destroy it. Nothing can show more clearly than this, that, although in accordance with received opinions, the second sound depends on closure of the semilunar valves, it is not formed by vibration of the valves, but by a con- cussion in the blood itself. Moreover, the possibility of the latter in case of the second sound proves the same possibility in case of the first sound, and should be a sufficient answer to those who allege that no concussion can occur between blood issuing from the ventricles and that in the vessels.* It has been previously pointed out, that one condition— force—^is here in excess as compared with that which occurs in the formation of the second sound, in which the more complete resistance presented by the closed valves makes amends. The first sound is usually loudest over the apex of the heart, and the second over the commencement of the aorta, but it is also heard very clearly in the track of the aortic arch. This accords with the present explanation; for since the first sound is formed by the meeting of blood expelled from the ventricles with that in their outlet vessels, it is easily conducted downwards by blood still in the ventricles, and is at the same time intensified by their solid walls; while contact of the apex of the heart with the interior of the chest causes the corresponding external point to be that at which the sound is most distinctly heard. The second sound, on the other hand, is formed at a time when no connexion exists between the blood in the ventricles and that in the vessels ; its conduction downwards is therefore interfered with, but it is heard with much distinctness for some distance in the track of that vessel at whose base it is mainly formed. The relation of inferior and superior—names proposed for the sounds of the heart by M. Pigeaux—is thus accounted for. * This objection lias been made to my explanation of the first sound by a reviewer in the British and Foreign Medico-Chirurgical Review, April, 1860.
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