THE CIRCULATION OF THE BLOOD AND LYMPH 83 



impulse. Marey's cardiograph (Fig. 22) consists essentially of a small 

 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 communi- 

 cated 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 corre- 

 sponding 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 por- 

 tion of the curve ; it is alone felt by the palpating hand, and the 

 auricular elevation is often absent from the cardiogram in man. 

 The rise is maintained, with small secondary oscillations, for about 

 o'3 of a second in a tracing 

 from a normal man, then 

 gives way to a sudden de- 

 scent, that marks the relax- 

 ation of the ventricles, the 

 beginning of the second sound, 

 and the closure of the semi- 

 lunar valves. An interval of 

 about o'5 second elapses be- 

 fore the curve begins again 

 to rise at the next auricular 

 contraction. 



Such was the interpretation 

 which Chauveau and Marey FlG 23 ._ CARDIOGRAM TAKEN WITH 

 put upon their tracings. Al- MAREY'S CARDIOGRAPH. 



though neither their results 



nor their deductions from A, auricular systole ; V, ventricular sys- 

 them have escaped the criti- tole ; D, diastole. The arrow shows the 

 cism of succeeding investiga- direction in which the tracing is to be read, 

 tors, it is doubtful whether 



any adequate reason has been brought forward for discarding 

 them, and Chauveau has recently furnished fresh 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 



Lpplied 

 impulse, the stem being connected with the recording tambour. In 



62 



