606 



HEART. 



distention of the auricle, as any one may easily 

 satisfy himself by repeating the experiment, 

 liesides, the distention of the auricles by the 

 blood flowing along the veins is too gradual for 

 this sudden and rapid impulse of the heart ; 

 nay more, the impulse may be observed when 

 no blood is flowing into the auricles. Sabatier* 

 believed that this impulse depends upon two 

 causes, 1st, principally upon the distention of 

 the auricles, more particularly the left; and, 

 2dly, upon the curvature of the large arteries. 

 Apparently, however, perceiving the necessity 

 of there being a sudden distention of the auri- 

 cles to produce this, he supposed that this was 

 effected by the auriculo-ventricular valves. He 

 argued that, as these valves during the diastole 

 of the heart form a cone stretching from the 

 base towards the point of the ventricle, which 

 is full of blood when the systole commences, 

 when the valves are carried upwards to ob- 

 struct the auriculo-ventricular orifices, this 

 blood is pushed before them into the auricles, 

 producing a reflux into the auricles, which, 

 with the blood flowing along the cavoe and pul- 

 monary veins, causes a sudden distention of the 

 auricles, which pushes the ventricle forwards. f 

 Meckel appears to have adopted the opinions 

 of Sabatier. We need not repeat our objec- 

 tions to this explanation. Dr. Alison, per- 

 ceiving the insufficiency of all these explana- 

 tions, has for a considerable time past sug- 

 gested in his lectures, that this might be ex- 

 plained by the arrangement of the fibres, 

 " more particularly by the irregular cone which 

 they form, being flattened posteriorly, and by 

 the consequent greater mass of fibres on the 

 anterior surface." More lately Mr. Carlisle J 

 has also attempted to explain this by the greater 

 length of the anterior fibres of the heart than 

 of the posterior. As the shape of the ventricles 

 is an oblique cone, and as they have their long- 

 est sides in front, he argues, " that it is a 

 law of muscular contraction that fibres are 

 shortened during their contraction in proportion 

 to their length when relaxed. For instance, if 

 a fibre one inch long lose by contraction one- 

 fourth of its length, or one quarter of an inch, a 

 fibre two inches in length will lose one inch by 

 contractions of equal intensity. The apex then 

 does not approach the base in the line of the 

 axis of the ventricles, but is drawn more to the 

 side of the longer fibres, that is, towards the 

 front, thus producing the tilting forwards." 

 We believe that it may be proved on mechani- 

 cal principles, that though the anterior and left 

 surfaces of the ventricles are considerably longer 

 than those on the posterior and right, yet during 

 their contraction, when they are drawn towards 

 their fixed attachments, if the fibres are of 

 equal thickness, the apex will be drawn up 

 nearly in the diagonal of the two forces, and 

 that if any tilting upwards of the apex take 

 place, this will be only to a small extent, and 



! * Traitc complet d'Anatomie, torn. ii. p. 230. 



t Dr. Bostock has failed of his usual accuracy 

 in detailing the opinion of Sabatier on this ques- 

 tion. 



t Transactions of British Scientific Association, 

 vol. iii. Dublin Journal of Medical Science, vol. iv. 



be quite insufficient to account for the impulse 

 felt at the chest. We must therefore look to 

 some other circumstances besides a mere diffe- 

 rence in length of the two surfaces to account 

 for this. Mr. Alderson* has ingeniously at- 

 tempted to apply the law of action and reaction 

 between bodies, one of considerable import- 

 ance in mechanical philosophy, and upon which 

 Barker's centrifugal mill has been constructed. 

 Unfortunately, however, for this explanation, 

 the axes of the large arteries and the direction 

 in which the apex is tilted do not by any means 

 accord. Dr. Hope's supposition that " the re- 

 tropulsion of the auricular valves" may assist 

 in producing this impulse, " as these act on a 

 column of blood which offers a greater resist- 

 ance than the weight of the heart, the action is 

 reflected on the organ itself and impels it for- 

 wards," is, on the other hand, completely op- 

 posed to the law that action and reaction are 

 the same. As well may a man attempt to pro- 

 pel a boat by standing in the stern, and push 

 with an oar against the prow. Dr. Filhos attri- 

 buted the impulse to the spiral turns of the 

 fibres at the apex of the heart attempting to 

 straighten themselves during their contraction, 

 and so raise themselves suddenly and throw 

 themselves forwards. The objections to this 

 explanation are so palpable that they must 

 occur to every one. Since the tilting of the 

 apex of the heart forwards is observed after the 

 blood has ceased to flow through its cavities, it 

 is obvious that we must look for the cause of 

 this in the arrangement of the muscular fibres 

 themselves, though it may be difficult to point 

 out that particular arrangement. It appears to 

 me that the distribution of some of the strong 

 bands of fibres, the course of which I have 

 already described when treating of the muscu- 

 lar tissue of the heart, may satisfactorily account 

 for it. We there pointed out that several strong 

 bands of fibres arise from the base of the septum 

 between the ventricles, pass downwards and 

 form part of the septum, then emerge from the 

 anterior longitudinal groove (fig. 274, d), and 

 wind round in a spiral manner to form both the 

 anterior and posterior part of the lower portion 

 of the heart. On entering the apices of the 

 ventricles, (principally the left,) the fibres are 

 scattered over their inner surfaces, and while a 

 great number of them go directly to be inserted 

 into the tendinous rings, others form part of the 

 columnar carnes. We have thus strong bands 

 of fibres attached by one extremity (their septal 

 extremity) to the base of the ventricles at a 

 point pretty far posterior, while at the other ex- 

 tremity many of the fibres are loose, or at least 

 only attached to the tendinous rings through 

 the media of the chorda tendinea; and valves, 

 which must admit of a certain degree of con- 

 traction of these fibres before they become tense. 

 At each systole of the heart when these fibres 

 act, it is evident that the tendinous rings must 

 form the fixed points towards which all these 

 fibres contract ; and since they are by one ex- 

 tremity all closely and directly connected to a 



* Quarterly Journal of Science. &c. vol. xviii. 

 p. 223. 



