Physiology and biochemistry in modern medicine . t natural method for demonstrating such apossibility would be to observe the effect on the heartbeat of some blockbetween the sinus and the rest of the heart. Such a block can be intro-duced in the heart of cold-blooded animals by local compression aroundthe various junctions. If a thread is tied around the sinoauricularjunction, the sinus will go on beating uninterruptedly, but the auriclesand ventricles—that is, the greater part of the heart below the ligatures—will cease beating, sometimes entirely (Stannius ligature). After awhile, however,
Physiology and biochemistry in modern medicine . t natural method for demonstrating such apossibility would be to observe the effect on the heartbeat of some blockbetween the sinus and the rest of the heart. Such a block can be intro-duced in the heart of cold-blooded animals by local compression aroundthe various junctions. If a thread is tied around the sinoauricularjunction, the sinus will go on beating uninterruptedly, but the auriclesand ventricles—that is, the greater part of the heart below the ligatures—will cease beating, sometimes entirely (Stannius ligature). After awhile, however, the heart below the ligature will usually begin to beat,but at a rhythm which is slower than, and independent of, that of thesinus. T1IK PHYSIOLOGY OF Till: HEARTBEAT 175 The experiment can be still better performed by usimj; a wedge-shaped clamp. (Gaskells clamp.) If ihis is applied so that the heartcan be pinched cither at the sinoauiicular junction or at the auriculo- ventricnlar, it will he found that, as the cardiac tissue is gradually. Fig. 42.—Heart-block produced by applying clamp at a-v junction. The clamp was tightened at a. (From Brubaker.) pinched, the portion of the heart below fails to heat as quickly as thatabove the clamp (Fig. 42). This is known as partial heart-block, andthe degree of the block is indicated by the numerical expression 2 to 1,3 to 1, 4 to 1, etc., meaning that the sinus is beating either twice asquickly as the ventricle, or three times, or four times as the case may
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