THE MOVEMENTS OF THE HEART. 57 



muscle. Ligature of one artery first affects the corresponding ventricle, then the 

 other ventricle, and, last of all, the auricles. Hence, compression of the left 

 coronary artery, (with simultaneous artificial respiration in a curarised animal), 

 causes slowing of the contractions, especially of the left ventricle, whilst the right 

 one at first contracts more quickly, and then, gradually its rhythm is slowed. 

 The contractions of the left ventricle are not only slowed but also weakened, whilst 

 the right pulsates with undiminished force. Hence it follows that, as the left half 

 of the heart cannot expel the blood in sufficient quantity, the left auricle becomes 

 filled, whilst the right ventricle, not being affected, pumps blood into the lungs. 

 (Edema of the lungs is produced by the' high pressure in the pulmonary circulation, 

 which is propagated from the right heart through the pulmonary vessels into the 

 left auricle {Samuelson and Griinhagen). According to Sig. Mayer, protracted 

 dyspnoea causes the left ventricle to beat more feebly sooner than the right, so that 

 the left side of the heart becomes congested. Perhaps this may explain the 

 occurrence of pulmonary oedema during the death-agony. 



Cohnheim and v. Schulthess-Rechberg found, after ligature of one of the large branches of a 

 coronary artery in a dog, that at the end of a minute the pulsations become intermittent. 

 This intermittence becomes more pronounced, the two sides of the heart do not contract 

 simultaneously (arhythmia), the heart beats more slowly, and the blood-pressure falls. 

 Suddenly, about 105 seconds after the ligature is applied, both ventricles cease to beat, and 

 there is a great fall of the blood-pressure. After an arrest lasting for 10 to 20 seconds, 

 twitching movements occur in the ventricles, while the auricles pulsate regularly, and may 

 continue to do so for many minutes, but the ventricles cease to beat altogether after 50 seconds. 

 According to Lukjanow, there is a peristaltic condition which operates upwards and downwards, 

 and occurs in the period between the regular contraction and the twitching vibratory move- 

 ment, Stimulation of the vagus does not arrest these peristaltic movements. 



Pathological. In so-called sclerosis of the coronary arteries in old age, there are attacks of 

 diminished cardiac activity, weakness of the heart, an altered rhythm and frequency, with 

 consequent breathlessness ; there may also be loss of consciousness, congestions, and attacks 

 of pulmonary oedema. Death may take place unexpectedly from sudden arrest of the heart's 

 action. 



48. MOVEMENTS OF THE HEART. Cardiac Revolution. The movement 

 of the heart is characterised by an alternate contraction and relaxation of its walls. 

 The total cardiac movement is called a " cardiac revolution," or a " cardiac 

 cycle," and consists of three acts the contraction or systole of the auricles, the 

 contraction or systole of the ventricles, and the pause (fig. 50). During the pause, 

 the auricles and ventricles are relaxed ; during the contraction of the auricles the 

 ventricles are at rest ; whilst during the contraction of the ventricles the auricles 

 are relaxed. The rest during the phase of relaxation is called the diastole. The 

 following is the sequence of events in the heart during a cardiac revolution : 



(A) The "blood flows into the auricles, and thus distends them and the auricular 

 appendices. This is caused by 



(1) The pressure of the blood in the venae cavae (right side) and the pulmonary 

 veins (left side) being greater than the pressure in the auricles. (2) The elastic 

 traction of the lungs ( 68), which, after complete systole of the auricles, pulls 

 asunder the now relaxed and yielding auricular walls. The auricular appendages 

 are also filled at the same time, and they act to a certain extent as accessory 

 reservoirs for the large supply of blood streaming into the auricles. 



(B) The auricles contract, and we observe in rapid succession 



(1) The contraction and emptying of the auricular appendix towards the atrium. 

 Simultaneously the mouths of the veins become narrowed, owing to the contraction 

 of their circular muscular fibres (more especially the superior vena cava and the 

 pulmonary veins) ; (2) the auricular walls contract simultaneously towards the 

 auriculo-ventricular valves and the venous orifices, whereby (3) the blood is 

 driven into the relaxed ventricles, which are considerably distended thereby. 



The contraction of the auricles is followed by 



