The physiology of the circulation in plants : in the lower animals, and in man : being a course of lectures delivered at surgeons' hall to the president, fellows, etc of the Royal college of surgeons of Edinburgh, in the summer of 1872 . Figs. 141,142, and 143, show the mitral (r s) and tricuspid (min) valves in action (human):how the segments, acted upon by the spiral columns of blood, roll up from beneath towardsthe end of the diastole (Fig 141) • how, at the beginning of the systole, they are wedged andtwisted into each other, on a level with the auriculo-ventricular orifices (Fig. 142); an
The physiology of the circulation in plants : in the lower animals, and in man : being a course of lectures delivered at surgeons' hall to the president, fellows, etc of the Royal college of surgeons of Edinburgh, in the summer of 1872 . Figs. 141,142, and 143, show the mitral (r s) and tricuspid (min) valves in action (human):how the segments, acted upon by the spiral columns of blood, roll up from beneath towardsthe end of the diastole (Fig 141) • how, at the beginning of the systole, they are wedged andtwisted into each other, on a level with the auriculo-ventricular orifices (Fig. 142); andhow, if the pressure exerted be great, they project into the auricular cavities (Fig. 143).When the mitral and tricuspid valves (Fig. 141, mm, op) are open, the aortic and pulmonicsemilunar valves (v w x, r s i)are closed. When, on the other hand, the mitral and tricuspidvalves are closed (Figs. 142, 143, and 144, r s, mi n), the aortic and pulmonic semilunar ones(v w x,r s t) are open. To this there is no exception.— Original. Fig. 143. Fig. Fig. 144 shows a human heart with a true mitral valve in both ventricles as seen inaction at the commencement of the systole. The letters are the same as in Figs. 141, 142,and 143.— Original. Note.—The spiral downward movement of the mitral and tricuspid valves (Fig. 141) hasonly been partly shown, from the difficulty experienced in representing spiral cavities. 1 This act take places just before the blood finds its way into the aorta andpulmonary artery, the amount of pressure recpuired for shutting and screwinghome the auriculo-ventricular valves being less than that required for raisingthe semilunar ones. PHYSIOLOGY OF THE CIRCULATION. 231 That the foregoing is the true explanation of the gradualapproximation and continued closure of the auriculo-ventricularvalves, there can, I think, be little doubt, both from the dispositionand structure of the parts, and from experiment. If, the coagulabe carefully removed from p
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