Elements of human physiology / by L. Hermann ; translated from the sixth edition by Arthur Gamgee.

  • Gamgee Arthur, 1841-1909.
Date:
1878
Catalogue details

Licence: Public Domain Mark

Credit: Elements of human physiology / by L. Hermann ; translated from the sixth edition by Arthur Gamgee. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    ever, is only when the pulse is of normal frequency, since any change in its rate only varies the duration of the diastole, whilst that of the systole remains con- stant. [It was found by Bonder?' in a large numher of ohservations, that whilst the duration of a complete cardiac revolution varied between 0-G40 and 0-806, the duration of ventricular systole fluctuated within very narrow limits, viz.! between 0-301 and 0-327.] The heart and large vessels lie within the thorax, in a spacious, closed chamber, which, together with the lungs, they tend to fill; in doing so they are dilated beyond their natural volume (see Chapter IV.); they are, therefore, under negative pressure, i.e. their walls (more especially those of the auricles and of the large veins which are most yielding) are drawn apart. The relaxed heart, therefore, tends to distend itself by sucking blood out of the veins. Owing to a special contrivance, the aspiration of blood through the veins is not even interrupted during the contraction of the ventricle—which must be looked upon as the heart-pump proper—but proceeds continuously. As the large veins open into the contractile auricles they possess a varying capacity. During the ventricular systole the auricles are relaxed, and are therefore in a position to receive the blood which is, in the meantime, sucked up into the thorax. During the diastole of the ventricles, on the other hand, blood flows into them from the then contracting auricles, without the passage of blood through the veins into the auricles being inter- rupted. The auricle must therefore not be considered as a pre- liminai-y suction- and force-pump, whose action is followed by that of a second pump, the ventricle, but is to be looked upon merely as a reservoir which regulates the pressure of blood in the venous system. Each lateral half of the heart, therefore, being a simple suction- and force-pump, merely requires a valvular arrangement at its orifice of entrance and exit; the first is formed by the auriculo-ventricular, the second by the semilunar valves. During the systole of the auricles the blood is sucked into the synchro- nously relaxed ventricle by the aspiration of the thorax (aided, perhaps, by the active power of aspiration exerted by the ventricle in its diastole, and to which we shall afterwards refer), so that no valves are required to prevent its reflux into the venous trunks. It is only the coronary veins which empty themselves into the right auricle, and whose contents being regulated, not by atmo- spheric, but by intra-thoracic pressure, require a valvular arrange- ment, and this is provided for by the so-called valvula Thehesii. The auricular cavities are never completely obliterated during Contraction, though this appears to be the case with the auricular appendages. . 1 Dondei-s, De Bhythmus der Hartstoonen. Nederlandsch. Archief voor Genets- en Nutui^^ kunde, 1865, p.-139. Translated in full by Dr. Moore in Dub. Quart. Journ. of Med. Sc vol. xlv. p. 225.. V