CHAP. VII 



MECHANICS OF THE HEART 



181 



i, 1649), t licit of pre-systole by Spring, I860, who, however, intended 

 1o describe an imaginary active dilatation of the ventricle, immediately 

 preceding systole. 



Normally the duration of presystole is much shorter than 

 that of systole. With accelerated cardiac rhythm, i.e. when the 

 period of the cardiac cycle decreases, perisystole, more particularly, 

 shortens, and shows a tendency to disappear altogether ; the 

 duration of systole, on the other hand, is either unchanged 

 (Ludwig), or shortens only 

 when there is an exag- 

 gerated acceleration of 

 rhythm (Donders). 



Presystole consists in a 

 contraction of the mus- 

 cular walls of the auricles, 

 seen with the unaided eye 

 to be peristaltic ; this peri- 

 stalsis starts from the 

 extreme end of the veins 

 which open into the aur- 

 icle, is propagated in the 

 auricle from above down- 

 wards, and extends as far 

 as the auriculo- ventricular 

 groove. The presystolic 

 contraction diminishes the 

 cavity of the auricles in 

 every diameter, least, how- 

 ever, in the longitudinal 

 direction (Kiirschner). 



The striated muscle 

 fibres with which the 

 veins are provided in the 

 vicinity of their openings 

 into the auricle, and the 

 arrangement of the mus- 

 cular fibres of which the 

 walls of the auricles con- 

 sist (Figs. 50, 51), account for the changes in diameter exhibited 

 in presystole. 



In systole, the ventricles seem on simple inspection to contract 

 simultaneously at every point. Yet more delicate observation 

 shows that the contraction here also is peristaltic, commencing at 

 the auriculo-ventricular groove, when the presystolic movement 

 has reached its maximum, and spreading thence to the apex with 

 such velocity that the eye cannot follow it. Systole is accordingly 

 only a continuation of the presystolic contraction wave, which 



Fir;. "iO. Human heart dissected after bulling, to show 

 superficial muscular fibres, seen anteriorly. (Allen 

 Thomson.) a', Aorta : >>', pulmonary artery cut short 

 close to semilunar valves, to show anterior fibres of 

 auricles : a, superficial layer of fibres of right ventricle ; 

 b, that of left : c, c, anterior interventricular groove ; rf, 

 right auricle ; <!', its appendix, both showing chiefly 

 perpendicular fibres ; < . upper part of left auricle ; 

 between e and // the transverse fibres, which, behind 

 the aorta, pass across both auricles ; t', appendix of 

 left auricle ; /. superior vena cava round which, near 

 the auricle, circular fibres are seen ; g, cf, right and left 

 pulmonary veins with circular bands of fibres surround- 

 ing them 



