312 CIRCULATORY SYSTEM. 



cardiac movement, which immediately follows the stage of rest, 

 occurs in the auricles, in the region of the openings of the vense 

 cavae on the right side, and of the pulmonary veins on the left ; 

 that this movement is propagated along the auricles in the direc- 

 tion of the ventricles ; and that by the time it has reached the 

 auriculo ventricular orifices it has ceased at the orifices of the 

 veins, and the muscular tissue in this region has begun to relax. 

 It is to be noted that the auricles act synchronously, so that 

 whatever is the condition of one auricle as to relaxation or con- 

 traction of its muscular tissue, the same condition exists in the 

 other. This contraction of the auricles is spoken of as the 

 auricular systole, and has something of a peristaltic character, 

 which has already been studied in connection with the stomach 

 and small intestine, although differing materially in that it is much 

 more rapid. 



Up to this time the ventricles are relaxed, or in a condition 

 of diastole; but as soon as the auricular contraction reaches 

 the ventricles these organs take it up, although in a different 

 manner. For, while in the auricles one portion is contracting 

 while another is relaxing, in the ventricles the whole mass of 

 muscle contracts at once with a degree of suddenness and vigor 

 which might be expected of so large a mass of striped muscular 

 tissue. This contraction is the ventricular systole, and while it is 

 taking place the auricles are relaxing throughout ; this relaxation 

 constitutes the auricular diastole. Thus the auricular systole and 

 ventricular diastole, and the auricular diastole and ventricular 

 systole, are respectively synchronous. Immediately after the 

 systole of the ventricles these structures relax, and for a brief 

 period the whole heart, both auricles and both ventricles, is in a 

 state of relaxation ; this is the pause of the heart. The work 

 performed by the ventricles is so much more important than that 

 of the auricles that when the terms systole and diastole are used, 

 reference is always had to these states of the ventricles, the 

 auricles being practically ignored. To designate the corresponding 

 states of the auricles it is always necessary to speak of the auricular 

 systole and diastole. 



Cardiograph. The cardiograph is an instrument for recording 

 the movements of the heart, the record itself being a cardiogram. 

 The form most used is that of Marey. It consists of a metal 

 box, over the mouth of which an elastic membrane is stretched, 

 to which a knob is attached (Fig. 163). This knob, in another 

 form of this instrument, is attached to a spring (Fig. 164). This 

 box or tympanum is in connection with another box, the recording 

 tambour, by means of a tube, and upon the elastic membrane of 

 this rests a lever. The first tambour is so fixed in place against 

 the chest wall as to bring the knob over the point where the 

 cardiac impulse is felt, and the movement of the knob is com- 



