MECHANICS OF THE HEART- BEAT 91 



chamber, or tambour, filled with air, and closed at one end by a flexible 

 membrane carrying a button, which can be adjusted to the wall of the 

 chest. This receiving tambour is connected by a tube with a recording 

 tambour, the flexible plate of which acts upon a lever writing on a 

 travelling surface a uniformly-rotating drum, for example covered 

 with smoked paper. Any movement communicated to the button 

 forces in the end of the tambour to which it is attached, and thus 

 raises the pressure of the air in it and in the recording tambour; the 

 flexible plate of the latter moves in response, and the lever transfers 

 the movement to the paper. The tracing, or cardiogram, obtained in 

 this way shows a small elevation corresponding to the auricular systole, 

 succeeded by a large abrupt rise corresponding to the beginning of 

 the first sound, and caused by the ventricular systole. This ventricular 

 elevation is the essential portion of the curve; it is alone felt by the 

 palpating hand, and the auricular elevation fs often absent from the 

 cardiogram in man. The rise is maintained, with small secondary 

 oscillations, for about 0*3 of a second in a tracing from a normal man, 

 then gives way to a sudden de- 

 scent, that marks the relaxation 

 of the ventricles, the beginning 

 of the second sound, and the 

 closure of the semilunar valves. 

 An interval of about 0-5 second 

 elapses before the curve begins 

 again to rise at the next auricular 

 contraction. 



Such was the interpretation 

 which Chauveau and Marey put 

 upon their tracings. Although 

 neither their results nor their 

 deductions from them have Fl g- 28. -Cardiogram taken with Marey's 

 escaped the criticism of succeed- Cardiograph A, auricular systole; 

 ing investigators it is doubtful ^ STr. ^ t ectSn in^hich 

 whether any adequate reason the tracing is to be read, 

 has been brought forward for 



discarding them, and Chauveau has furnished further proofs of their 

 accuracy. The difficulties that beset the subject are great, for the 

 cardiogram is a record of a complex series of events. The very rapid 

 variation of pressure within the ventricles, the change of volume and 

 of shape of the heart, the slight change of position of its apex, must 

 all leave their mark upon the curve, which is besides distorted by the 

 resistance of the elastic chest-wall, the inertia of the recording lever, 

 and the compression of the air in the connecting tubes. It is only by 

 comparing in animals the cardiographic record with the changes of 

 blood-pressure in the heart and arteries that our present degree of 

 knowledge of the human cardiogram has been attained. Could we 

 register directly the fluctuations of pressure in the interior of the human 

 heart, the cardiographic method would be rarely employed. For 

 clinical purposes the receiving tambour can be advantageously replaced 

 by a small glass funnel or a small metal cup, the open end of which is 

 applied without a membrane over the cardiac impulse, the stem being 

 connected with the recording tambour. In cases in which the right 

 ventricle is in contact with the chest-wall at the position of the apex- 

 beat the cardiogram is ' inverted ' that is to say, the chest-wall is 

 drawn in during systole and protruded during diastole of the ventricles. 

 Inversion of the cardiogram is, therefore, not an infallible sign of the 

 pathological condition known as adherent pericardium (Mackenzie). 



