246 PHYSIOLOGY OF THE HEART [CH. XXL 



from clear, and the extent of each varies considerably even in health, 

 but in heart disease the electro-cardiogram shows very marked 

 differences from the normal, especially in cases of "heart-block." 

 When in the future the meaning of each part of the record is under 

 stood, the physician will be provided with a new help to diagnosis. 



FIG. 227. Electro-cardiogram obtained by photographing the movements of the thread of a String 

 Galvanometer. The electrodes were connected to a man's right and left hands. Waves upwards 

 indicate that the base (right ventricle) is galvanometrically negative to the apex (left ventricle) ; 

 downward waves have the opposite meaning. Wave P accompanies auricular systole ; waves 

 Q, R, S, and T occur during ventricular systole. The time- tracing (T) shows tenths of a second. 

 (After Einthoven.) 



The Cardiophonogram. An interesting extension of this work 

 consists in the registration of the heart sounds. This was first done 

 by Hiirthle some years ago, but Einthoven's string galvanometer, as 

 an instrument of precision far exceeding these previously used, 

 has enabled him to repeat this work with much greater accuracy. A. 

 stethoscope is placed over the chest and connected to a microphone, 

 which magnifies the heart sounds ; the vibrations in the microphone 

 are communicated as electrical changes by a transformer to the 

 string galvanometer, the movements of the quartz fibre being finally 

 photographed on a travelling plate. If simultaneously an electro- 

 cardiogram is taken, the simultaneity of the first heart sound with 

 the ventricular systole, and of the second heart sound with the com- 

 mencement of ventricular diastole, are very conclusively demon- 

 strated. In heart disease where the adventitious sounds called 

 murmurs are present, their time relationships in the cardiac cycle 

 are most clearly seen. 



Einthoven has further found the presence of a third heart sound, which is 

 inaudible to the unaided ear, although it was first described by Dr A. G. Gibson 

 of Oxford, in a patient in whom it was very pronounced, by means of ordinary 

 auscultation. It seems, however, to be present in all human hearts in varying 

 degrees of intensity when the cardiophonogram is examined. It occurs during 

 diastole, and follows the second sound after a short pause. It is not due to a 

 reduplication of the second sound, nor is it a presystolic murmur such as can be 

 heard in man when there is obstruction at the auriculo-ventricular orifices. 

 Einthoven adduces evidence against both these views, and believes it is produced 

 at the aortic orifice ; the semilunar valves and the neighbouring portion of the 

 aortic wall being thrown for a second time and for a short period into vibration 

 by the changes in the aortic pressure which occur during diastole. 



