THE CIRCULATION OF THE BLOOD 2?5 



vertically from the middle of the clavicle. The cardiac impulse is synchron- 

 ous with the cardiac systole. 



The cardiac impulse may be recorded with an appropriate apparatus 

 known as a cardiograph; the record obtained with it is known as a cardiogram 

 A cardiograph consists of a tambour covered with a thin rubber membrane 

 provided with a button. The tambour is supported by a metallic frame 

 which permits of an easy and accurate adjustment of the button over the 

 seat of the; cardiac impulse. A rubber tube connects the cardiographic 

 tambour with a second tambour provided with a recording lever and thus 

 transmits all variations in the pressure of the air in the former to the latter 



When all adjustments are carefully made a tracing similar to that shown 

 in Fig. 118 will be obtained, in which the slight elevation a represents the 

 contraction of the auricle which, completing 

 the filling of the ventricle, causes the apex of 

 the heart to press more vigorously against the 

 chest wall; b-c represents the contraction of 

 the ventricles, at which moment the apex is 

 suddenly and forcibly driven against the chest 

 wall; c-d represents the systolic plateau, the 

 time during which the ventricle is discharging 

 blood into the aorta; d-e represents the relaxa- 

 tion of the ventricle; while e-f represents the 

 time of the diastole, during which the heart 

 cavities are enlarging with the incoming of a FIG. n8. A CARDIOGRAM. 

 new volume of blood in consequence of which (After Faction.) 



the heart is pressing against the chest walls. The systolic plateau is charac- 

 terized by one or more elevations and depressions, the true cause of which is 

 unknown. 



The Cardiac Cycle. The term cardiac cycle is employed to express the 

 sequence of events from the beginning of one auricular systole and the 

 beginning of the auricular systole which immediately follows it. An examina- 

 tion of the heart shows that each pulsation may be divided into three phases, 

 viz. : 



1. The auricular systole. 



2. The ventricular systole. 



3. The pause or period of repose during which both auricles and ven- 



at rest. 



The Graphic Record of the Cardiac Cycle. For the purpose of obtaining accurate in- 

 formation as to the sequence of events, their time relations, as well as of the pressure within the 

 heart cavities during each phase of its activity, it is necessary to obtain graphic records of the 

 entire cardiac cycle. 



This was first successfully accomplished by Chauveau and Marey, by means of sounds or 

 tambours (Fig. 119) introduced through the jugular vein into the cavities of the right heart. Each 

 tambour consists of a metallic frame covered by a thin rubber membrane. By means of flexible 

 tubes, a. v., the interior of each tambour can be placed in communication with the interior 

 of a second tambour provided with a recording lever. Pressure applied to the cardiac tambour 

 will be followed by a movement of the enclosed air toward the recording tambour indicated 

 by an outward movement of its membrane and a rise of the lever; removal of the pressure will 

 be followed by a movement of the enclosed air toward the cardiac tambour indicated by an 

 inward movement of the membrane and a fall of the lever. 



When the tambours are introduced into, and carefully adjusted to the interior of the right 

 heart, the auricular and ventricular contractions will exert pressure on their enclosed tambours 

 as indicated by the rise of the levers of the recording tambours, which continues so long as 

 the pressure lasts. With the relaxation of the auricular and ventricular walls the pressure is 



