RHYTHM OF THE HEART. 113 



of the right side determines or regulates that of the left, or 

 vice versd; and we must suppose that when they act together 

 in the perfect heart, it is because they are both, as it were, set 

 to the same time. Neither can we say that the auricles deter- 

 mine the action of the ventricles ; for, if they are separated, 

 they will both contract and dilate in regular, though not nec- 

 essarily similar, succession. A fact pointed out by Mr. Mai- 

 den shows how the several portions of each cavity are similarly 

 adjusted to act alike, yet independently of each other. If a 

 point of the surface of the ventricle of a turtle's or frog's heart 

 be irritated, it will immediately contract, and very quickly 

 afterwards all the rest of the ventricle will contract ; but, at 

 the close of this general contraction, the part that was irritated 

 and contracted first, is slightly distended or pouched out, show- 

 ing that it was adjusted to contract in, and for only, a certain 

 time, and that therefore as it began to contract first, so it began 

 to dilate first. 



The best interpretation, perhaps, yet given of it, and of 

 rhythmic processes in general, is that by Mr. Taget, who re- 

 gards 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 in- 

 stability 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 con- 

 traction. According to this view, there is in the nervous 

 ganglia of the heart, and in all parts originating rhythmic pro- 

 cesses, 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 ex- 

 hibited in the action of the heart, are but well marked ex- 

 amples of such chrouometric 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 influences con- 

 veyed from without, through branches of the pueumogastric 

 and sympathetic nerves. 



The pneumogastric nerves are the media of an inhibitory or 

 restraining influence over the action of the heart ; for when by 

 section their influence is withdrawn, the pulsations of the 

 organ are increased in frequency and strength ; while an oppo- 

 site effect is produced by stimulating them, the transmission 

 of an electric current of even moderate strength diminishing 

 the pulsations, or stopping them altogether. Stimulation of 



