FREQUENCY OF THE HEART'S ACTION. 51 



sternum has been removed. Under these conditions, the first sound loses its booming 

 c.haracter, retaining, however, the muscular element, when the instrument is applied to 

 the exposed organ. 



The first sound of the heart is complex. It is produced by the sudden closure of the 

 auriculo-ventricular valves at the beginning of the ventricular systole, to which are super- 

 tulded, the muscular sound, due to the contraction of the muscular fibres of the heart, and 

 the impulsion-sound, due to the shock of the organ against the walls of the thorax. 



The second sound is simple. It is produced by the sudden closure of the aortic and 

 ptilmonic semilunar valves, immediately following the ventricular systole. 



It is of the greatest importance, with reference to pathology, to have a clear idea of 

 the currents of blood through the heart, with their exact relation to the sounds and 

 intervals. At the commencement of the first sound, the blood is forcibly thrown from 

 the ventricles into the pulmonary artery on the right side and the aorta on the left, 

 and the auriculo-ventricular valves are suddenly closed. During the entire period oc- 

 cupied by this sound, the blood is flowing rapidly through the arterial orifices, and the 

 auricles are receiving blood slowly from the vena? cava3 and the pulmonary veins. When 

 the second sound occurs, the ventricles having become suddenly relaxed, the recoil of 

 the arterial walls, acting upon the column of blood, immediately closes the semilunar 

 valves upon the two sides. The auricles continue to dilate, and the ventricles are slowly 

 receiving blood. Immediately following the second sound, during the first part of the 

 interval, the auricles become fully dilated ; and, in the last part of the interval, imme- 

 diately preceding the first sound, the auricles contract and the ventricles are fully 

 dilated. This completes a single revolution of the heart. 



Frequency of the Heart* 1 z Action. Physicians have always attached the greatest im- 

 portance to the frequency of the action of the heart, as one of the important indications 

 of the general condition of the system. The variations which are met with in health, de- 

 pending upon age, sex, muscular activity, the condition of the digestive system, etc., point 

 to the fact that the action of the heart is closely allied to the various functions of the 

 economy and readily sympathizes with their derangements. As each ventricular systole 

 is followed by an expansion of the arteries, which is readily appreciated by the touch, it 

 is more convenient to study the succession of these movements by exploring the vessels 

 than by examination of the heart itself. Leaving out certain of the qualities of the pulse, 

 this becomes an exact criterion of the acts of the heart. 



The number of pulsations of the heart is not far from seventy per minute in an adult 

 male and is from six to ten more in a female. There are individual cases, however, in 

 which the pulse is normally much slower or more frequent than this, a fact which must be 

 remembered when examining the pulse in disease. It is said that the pulse of Napoleon I. 

 was only forty per minute. Dr. Dunglison mentions a case which came under his own 

 observation, in which the pulse presented an average of thirty-six per minute. The same 

 author states that the pulse of Sir William Congreve was never below one hundred and 

 twenty-eight per minute, in health. It is by no means unfrequent to find a healthy pulse 

 of a hundred or more a minute ; but, in the cases reported in which the pulse has been 

 found to be forty or less, it is possible that every alternate beat of the heart was so feeble 

 as to produce no perceptible arterial pulsation. In this case, the fact may be ascertained 

 by listening to the heart while the finger is placed upon the artery. Such an instance has 

 lately come under our observation, in which the pulse was apparently but thirty-five p*.-r 

 minute. 



Influence of Age and Sex .In both the male and female, observers have constantly 

 found a great difference in the rapidity of the heart's action at different periods of life. 

 The observations of Dr. Guy upon this point are very many and were made with the 

 utmost care with regard to the conditions of the system at the time the pulse was taken 



