Graphic methods in heart disease / By John Hay ... ; with an introduction by James Mackenzie.

  • Hay, John A., 1942-
Date:
1909
Catalogue details

Licence: In copyright

Credit: Graphic methods in heart disease / By John Hay ... ; with an introduction by James Mackenzie. Source: Wellcome Collection.

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

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    the myocardium some functions are more highly developed than others ; for example, the function of stimulus production is most marked wherever there are remains of the sinus venosus, as at the opening of the great veins into the auricles and about the orifice of the coronary sinus. Of these sites, the junction of the superior vena cava with the right auricle is most active, and the result is, that the stimuli originating here initiate muscular contractions which spread from this point over the auricles and ventricles. The function of tonicity, possessed of course by all the fibres, is present in a high degree in the muscular fibres surrounding the valvular openings and the open- ings of the veins into the auricles ; while contractility is especially developed in the large thick walls of the ventricles. Thus we see that, though every fibre possesses in some degree all five characteristics, in certain groups of fibres one function is predominant. The most important fact about the myocardium is its reserve power. If the load of the heart be increased or the resistance to the flow of blood from the ven- tricles be augmented, the contraction of the muscle fibres becomes greater ; and in spite of the added difficulty, the action of the heart is efficient. The heart is thus enabled, within certain limits, to meet sudden and unusual calls upon its resources. When the heart fails to cope with the added stress,