298 OF THE CIRCULATION OF THE BLOOD. 



extraordinary tendency to rhythmical action, by which the heart is distin- 

 guished from nearly all other muscles, is shown by the fact, that not only 

 do the entire hearts of cold-blooded or of hibernating animals continue to 

 act long after their removal from the body, but even separated portions of 

 them will contract and relax with great regularity for a long time. 1 Thus 

 the auricles will persist in their rhythmical action, when cut off above the 

 auriculo-veutricular rings; and the apex of the heart will do the same, when 

 separated from the rest of the ventricle. There is strong reason for believ- 

 ing that the contact of the blood itself with the lining membrane of the 

 Heart is, as Haller maintained, the ordinary stimulus inciting it to contract. 

 As already stated, Schweigger-Seidel has observed a rich plexus of nerve- 

 h'bres in this membrane, whilst its sensitiveness to mechanical irritation was 

 incidentally shown by an experiment of Bernard, 2 in which the contact of 

 the bulb of a thermometer with the interior of the ventricles immediately in- 

 creased the number of pulsations. SchifP and Budge 4 have, moreover, shown 

 that the action of both auricles and ventricles rapidly ceases if they are placed 

 on blotting-paper; but that they may be called into action again, either by 

 immersing them in blood, or by dropping a little blood into their cavities. 

 And an ingenious experiment was made by Haller himself, showing that if 

 arrangements are made, by which either the right or left side of the Heart 

 remains filled with blood, whilst the other can discharge its contents and re- 

 mains empty, that side which is stimulated by the presence of the blood con- 

 tinues to beat rhythmically long after the movement of the other has ceased. 

 When the irritability of the heart is nearly exhausted, the usual rhythm is 

 often a good deal disturbed, so that the contractions of the auricles and ven- 

 tricles do not regularly alternate with each other; and one set frequently 

 ceases before the other. 



236. When the Heart is exposed in a living animal, and its movements 

 are attentively watched, they are seen to follow each other with great regu- 

 larity. In an active and vigorous state of the circulation, however, they are 

 so linked together, that it is not easy to distinguish them into periods; both 

 Auricles contracting, and also dilating, simultaneously; and both Ventricles 

 doing the same. The systole or contraction of the Ventricles corresponds 

 with the projection of blood into the arteries; whilst the diastole or dilatation 

 of the Ventricles coincides with the collapse of the arteries. The contrac- 

 tion of the Auricles and Ventricles run into each other, that of the Auricle 

 immediately preceding that of the Ventricle. The entire period that inter- 

 venes between one pulsation and another, is nearly equally divided between 



tion of the Uterus, Heart, and other rhythmically-acting organs, as well as indeed of 

 all muscular tissue, is the absence of oxygenated or arterial blood (Epilepsy, 3d edit., 

 p. 20etseq.) ; whilst Mr. Paget has endeavored to explain the phenomena by referring 

 them toan intermission in the processes of nutrition (Croonian Lecture. 18">7). LaMly, 

 v. Bezold, Untersuch. iib. d. Innervation des HJMv.ens, Leipzig, 18(>3, attributes the 

 contractions to continuous excitations originating in the cardiac excito-motory gan- 

 glia, which meeting with continuous resistances in the cardiac inhibitory ganglia 

 only periodically, that is to say, after overcoming such opposition act on the mus- 

 cular tissue. None of these theories, however, appear to afford a sufficient explana- 

 tion of all the facts, and the essential cause of the rhythmical action of the Heart 

 must still remain an unsolved question. 



1 Reid, indeed, was of opinion (Cyc. of Anat. and Physiology, vol. ii, p. 611), that 

 the rhythmical action of the heart in the frog could continue in the absence of any 

 physical stimulus, for he observed contractions taking place 1 even in vacuo ; but his 

 experiments have been repeated on several occasions with different results, the pulsa- 

 tions ceasing on the withdrawal of the air, and commencing again when it was read- 

 mitted. 



2 Lecons sur les Liquides de I'Organisme, 1859, p. 124. 



3 Vierordt's Archiv, 1850, p. 34. 4 Arehiv f. Phys. Heilk., 184G, p. 561. 



