HEART 429 



marked feature of visceral muscle (p. 215), and it is also 

 manifest in skeletal muscle (p. 211). It would, therefore, 

 be curious if it were absent in cardiac muscle. The rapid 

 rhythmic contraction makes it more difficult to investigate, 

 and some physiologists actually deny its existence and 

 maintain that tone of the heart muscle, which should 

 prevent over-distension, is rendered unnecessary by the action 

 of the fibrous pericardium. 



But there is considerable evidence that it does exist, and 

 that it plays a not unimportant part. Gaskell found in the 

 heart of cold-blooded animals that perfusing a fluid con- 

 taining a weak alkali gradually decreased the diastolic filling 

 and finally stopped the heart in S3^stole, while perfusing a 

 weak solution of lactic acid increased the diastole and 

 reduced the systole, and, finally, brought the heart to a 

 standstill in fidl diastole. Strophanthus acts like an alkali. 



Clinically a condition of over-distension of the heart is 

 frequently observed and the administration of strophanthus 

 is found to decrease the distension. Physicians generally 

 resjard this as due to loss of tone. Some investigators 

 maintain that it is simply due to too great diastolic filling, 

 with too great lengthening of the muscle fibres. 



Pathological Disturbances of Contraction and Conduction. 



(1) Heart-block. — Since, in the mammalian heart, 

 muscular continuity between auricles and ventricles through 

 the band of His is of small extent, the w^ave of 

 contraction is delayed at this point, and in the 

 dying heart and in various pathological conditions, the 

 contraction frequently fails altogether to pass this block, and 

 the ventricles do not contract after each auricular systole, 

 and may either stop, or contract only after two or three 

 auricular contractions have occurred. In such cases the 

 pulse rate is reduced to a half or even less of its normal 

 rate. A condition of bradycardia through "heart-block" is 

 produced. This condition is revealed by a study of the 

 pulse in the veins of the neck or by the electrocardiogram. 



(2) Auricular Flutter — Another condition in which the 



