. Kirkes' handbook of physiology . Fig. 169. Fig. 168.—The Heart of a Frog (Rana esculenta), from the Front. V, Ventricle; Ad, rightauricle; .4s. left auricle; B, bulbus arteriosus, dividing into right and left aorta?. (Ecker.) Fig. 169.—The Heart of a Frog (Rana esculenta), from the Back. 5. v., Sinus venosus opened;c. s. s., left vena cava superior; c. t. d., right vena cava superior; c. i., vena cava inferior; v. p.,vena pulmonales; .4. d., right auricle; A. s. left auricle; .4. p., opening of communication betweenthe right auricle and the sinus venosus. X 2^-3. (Ecker.) strips of the apex
. Kirkes' handbook of physiology . Fig. 169. Fig. 168.—The Heart of a Frog (Rana esculenta), from the Front. V, Ventricle; Ad, rightauricle; .4s. left auricle; B, bulbus arteriosus, dividing into right and left aorta?. (Ecker.) Fig. 169.—The Heart of a Frog (Rana esculenta), from the Back. 5. v., Sinus venosus opened;c. s. s., left vena cava superior; c. t. d., right vena cava superior; c. i., vena cava inferior; v. p.,vena pulmonales; .4. d., right auricle; A. s. left auricle; .4. p., opening of communication betweenthe right auricle and the sinus venosus. X 2^-3. (Ecker.) strips of the apex of the ventricle of the terrapin, which is free from the nervecells, at least nerve ganglia, and found that they contracted rhythmicallyfor hours. This experiment has become a classic one for the study of the car-. FlG. 170.—Automatic Contractions of Sinus Muscle from the Terrapins Heart in per centSodium Chloride. Time in minutes. (New figure by L. Frazier.) diac muscular tissue. Strips of cardiac muscle cut from the auricle andfrom the contractile walls of the venae cavae, or sinus venosus, of the terra-pin also contract rhythmically. If the strips of muscle are kept moist with thesame blood or serum, then the rhythm of the sinus is greater than that of the 175 THE CIKCUIiATION OF TFFK HUH) I) auricle, and that of the auricle greater than that of the ventricle, a differencethat is based on a physiological differentiation of the tissue. The sinusmuscle is also more delicately responsive to stim-uli than is the ventricular muscle, , it is moreirritable. Porter has performed the more difficult ex-periment of isolating a small disc of muscle fromthe ventricle of the dog, leaving only the delicatenutrient artery through which the muscle wasfed with defibrinated blood. This isolated smallp
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