. Elements of human physiology. Physiology. THE VASCULAK MECHANISM 233 Section 4 CAEDIAC EHYTHM If the heart be rapidly cut out of the body, it will con- tinue beating in a normal fashion for some time—in the case of mammals from five to ten minutes ; in the case of cold- blooded animals, such as the frog or tortoise, for some hours or even days. We say therefore that the rhythm of the heart is automatic ; and we have now to discuss wherein this automatic rhythmicity lies. The circumstance that the cold-blooded heart goes on beating so long, when severed from all connec- tion with the body, ha
. Elements of human physiology. Physiology. THE VASCULAK MECHANISM 233 Section 4 CAEDIAC EHYTHM If the heart be rapidly cut out of the body, it will con- tinue beating in a normal fashion for some time—in the case of mammals from five to ten minutes ; in the case of cold- blooded animals, such as the frog or tortoise, for some hours or even days. We say therefore that the rhythm of the heart is automatic ; and we have now to discuss wherein this automatic rhythmicity lies. The circumstance that the cold-blooded heart goes on beating so long, when severed from all connec- tion with the body, has caused it to be much used in investi- gations on the subject, and from it most of our knowledge has been acquired. Methods of Investigation The contractions of the frog's heart may be recorded by magnifying its movements by means of a light lever, one end of which rests upon the ventricle, while the other end is made Fig. Schiifei's heart plethysmograph. to write upon a blackened surface—or, as in Gaskell's method, by clamping the heart in the auriculo-ventricular groove, and attaching threads from auricle and ventricle to two levers which are arranged to write one over the other. Or we may register the changes in the intraventricular pressure by allowing dilute blood or some other nutrient fluid to flow through a perfusion cannula tied into the ventricle, and attaching the exit-tube of the cannula to a small mercurial manometer. Another way is to register the changes in volume of the. 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 resemble the original Starling, Ernest Henry, 1866-1927. Chicago : W. T. Keener
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