RHYTHM OF THE HEART. 141 



latter will cease to do so, and no rhythmic action can be, 

 by any means, excited in it. Other sections of the heart, 

 and experiments of other kinds, seem to show that the 

 cause of the rhythmic action of the ventricle, and probably 

 also of the auricles so long as they are associated with it, 

 is situated about the boundary-ring between the auricles 

 and ventricle ; for that which remains connected with this 

 part retains its rhythm, while that which is disconnected 

 from it loses rhythm. They seem to prove, also, that the 

 rhythm does not depend on the properties of the muscular 

 tissue alone or independently, but is derived from the 

 nervous ganglia, as so many centres of rhythmic action, 

 which are chiefly situated in the region named. "Why 

 these nervous centres should issue impulses for rhythmic 

 rather than for continuous action, is still a debateable point. 

 The most philosophical interpretation yet given of it, and 

 of rhythmic processes in general, is that by Mr. Paget, 

 who regards them as dependent on rhythmic nutrition, i.e., 

 on a method of nutrition in which the acting parts are 

 gradually raised, with time-regulated progress, to a certain 

 state of instability of composition, which then issues in the 

 discharge of their functions, e.g., of nerve-force in the case 

 of the cardiac ganglia, by which force the muscular walls 

 are excited to contraction. According to this view, there is 

 in the nervous ganglia of the heart, and in all parts 

 originating rhythmic processes, the same alternation of 

 periods of action with periods of repose, during which the 

 waste in the structure is repaired, as is observed in most 

 of, if not all, the organic phenomena of life. All organic 

 processes seem to be regulated with exact observance of 

 time ; and rhythmic nutrition and action, as exhibited in 

 the action of the heart, are but well-marked examples of 

 such chronometric arrangement. 



We may conclude, then, that the nervous ganglia in the 

 heart's substance are the immediate regulators of the 

 heart's action, but that they are themselves liable to in- 



