Carpenter's principles of human physiology . of which is closed by a thin india-rubber membrane called a tympanum. Tothe brass back a flat steel spring is screwed, which is bent twice at right anglesin such a way that its extremity is opposite the centre of the tympanum. Theextremity is perforated by a steel screw, the point of which rests on themembrane, whilst its head is surmounted by an ivory knob. The tympanumis provided with three adjusting screws, by which when in use it rests onthe wall of the chest with its face parallel to the surface, and can be approxi-mated or withdrawn at will. T
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Carpenter's principles of human physiology . of which is closed by a thin india-rubber membrane called a tympanum. Tothe brass back a flat steel spring is screwed, which is bent twice at right anglesin such a way that its extremity is opposite the centre of the tympanum. Theextremity is perforated by a steel screw, the point of which rests on themembrane, whilst its head is surmounted by an ivory knob. The tympanumis provided with three adjusting screws, by which when in use it rests onthe wall of the chest with its face parallel to the surface, and can be approxi-mated or withdrawn at will. The cavity of the disc communicates by avulcanized india-rubber tube with a second tympanum represented by b in * Annal. des Scien. Nat., 4th ser., Zool., torn. xvii. p. 374; and Mem. de la Soc. deBiol., ser. iii. torn. iii. pt. ii. 1862, p. 1. For other Cardiography tracings and accounts ofthe instruments employed, see A. H. Garrod in Journ. of Anat. and Phys., Nov. 1870, andRutherfords Lectures in Lancet, 1871-2. ACTION OF THE HEART. 283. Fig. 123 in such a way that the two tympana and the tube enclose an air-tight cavity. The movement of the second tympanum is magnified andinscribed on a registering cylinder by a lever. The causes of the impulseaccording to Sibson are, first—the rigidity of the mus- fig_ 123.cular walls during contraction; secondly, a lever move-ment forward, due to the thickening of the muscle, whichoccurs during contraction, being resisted by the fibrous bedof the pericardium on which the heart rests; and, lastly, the outward pressure of the blood in the ventricles on the walls by which it is expelled, and through those walls on theribs and intercostal spaces. 219. When the ear is ap-plied over the cardiac region, daring the natural move-ments of the Heart, two suc-cessive sounds are heard, eachpair of which correspondswith one pulsation ; there is Tracing obtained by the Cardiograph also an interval of silence ofMM.ChauveauandMarey between each recurrence,