1068 



PHYSIOLOGY 



galvanometer or electrometer, becomes negative twice in the course 

 of the cardiac contraction. 



We must conclude therefore that the ventricular systole is com- 

 parable with a simple muscular twitch and cannot be regarded as 

 the summation of several contractions. Since the excitatory process 

 extends in the form of a wave not only to all parts of the same cavity 

 but to all parts of the heart, it is evident that the musculature of the 



heart is to be compared, not 

 with skeletal muscle com- 

 posed of many fibres, but to 

 a single muscle fibre in which 

 all parts are in functional 

 continuity. 



THE BEAT OF THE 

 MAMMALIAN HEART 

 The mammalian heart, like 

 the heart of cold-blooded 

 animals, will beat for some 

 time after it has been cut out 

 of the body, and a perfectly 

 rhythmic activity may be 

 maintained for hours by 

 feeding the heart from the 

 coronary arteries either with 

 \ defibrinated blood or with 

 I oxygenated Ringer's solution, 

 I with or without the addition 



FIG. 432. Distribution of potential differences ( 



due to electrical variations in the beating UangilOH-cells are tound 



heart. (WALLER.) in the mamma li an heart 



To record the variations any of the points n . -, e 1-1 



a may be led off, together with any of the around the Openings of the 



P oillt8 & - great veins, along the border 



of the interauricular septum, 



in the groove between auricles and ventricles, and in the uppermost 

 parts of the*ventricles. 



The ventricles of mammals are endowed with a greater rhythmic 

 power than the corresponding cavities in the frog and tortoise. It is 

 possible to sever or crush all the nervous and muscular connections 

 between auricles and ventricles without destroying their mechanical 

 connection by means of fibrous tissue. Such a procedure does not, 

 even for a moment, stop the contractions of the ventricles, which go 

 on beating at a rhythm which is independent of and slower than that 

 of the auricles. Porter has shown that a mere fragment of the ventri- 



