. Elements of human physiology. Physiology. 242 PHYSIOLOGY Bhythm of Mammalian Heart So far as we know, the process of contraction in the mammalian heart is essentially the same as in the frog's heart. The contraction starts in the terminations of the great veins, and travels thence over the am-icles. A pause of about one-tenth of a second occurs, and then the ventricles contract, the contraction starting at the base and travelling thence as a wave to the apex. The wave-like progression of the excitatory condition in the ventricle can be well shown, as in the frog, by leading off the base and
. Elements of human physiology. Physiology. 242 PHYSIOLOGY Bhythm of Mammalian Heart So far as we know, the process of contraction in the mammalian heart is essentially the same as in the frog's heart. The contraction starts in the terminations of the great veins, and travels thence over the am-icles. A pause of about one-tenth of a second occurs, and then the ventricles contract, the contraction starting at the base and travelling thence as a wave to the apex. The wave-like progression of the excitatory condition in the ventricle can be well shown, as in the frog, by leading off the base and apex of the exposed ventricle to the two terminals of a capillary electrometer. We then get in many cases a diphasic variation differing only in the shorter dura- tion of its phases from that described for the frog's heart. We can in fact (as was shown by Waller) by leading off from the apex beat and right hand obtain a photographic record of the variation of the heart in man. Fig. 133 represents Fig. Hsi (to apex) Acid (to base) Pulse tracing from caroMd Electrical variation of human heart. (BayUss and Starling.) the variation of the ventricles as obtained in this way. It will be seen that the variation is triphasic, implying that the excitatory change starting at the base of the heart extends thence to the apex, but the contraction lasts longer at the base than at the apex. The production of the curve is shown by the following diagram (Fig. 134). With a more delicate electrometer it is possible to record also the electrical change due to the auricular contraction. This has the appearance of a sharp spike immediately pre- ceding the triphasic ventricular variation. The only essential difference between the mammalian and amphibian heart seems to lie in the comparative automaticity. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly r
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