76 THE MOVEMENTS OF THE HEART. 



pulsations become discontinuous; several, as it were, do not occur. This inter - 

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

 simultaneously (ar/iythmia), the heart beats more slowly, and the blood-pressure 

 falls. Suddenly, about 105 sees, after the ligature is applied, both ventricles cease 

 to beat, and there is the greatest fall of the blood-pressure. After 10 to 20 sees., 

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

 and may continue to do so for many minutes, while the ventricles cease to beat 

 altogether after 50 sees. According to Lukjanow, there is a peristaltic condi- 

 tion which operates upwards and downwards, and occurs in the period between 

 the regular contraction and the twitching vibratory movement. 



48. The Movements of the Heart. 



Cardiac Revolution. The movement of the heart is characterised by 

 an alternate contraction and relaxation of the cardiac 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. 

 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 : 



EVENTS DURING A CARDIAC REVOLUTION. 



(A.) The Blood Flows into the Auricles, and thus distends them and 

 the auricular appendages. This is caused by 



(1.) The pressure of the blood in the venae cavse (right side) and the 

 pulmonary veins (left side) being greater than the pressure in the 

 auricles. 



(2.) The elastic traction of the lungs ( 60) 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 (Haller, Nysten) 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 



