162 



THE CIRCULATION OF THE BLOOD 



tube to the interior of the second recording tambour, also closed, and through 

 the elastic and movable disc of the latter to the writing lever which is ad- 

 justed to a registering apparatus. This latter generally consists of a cylinder 

 or drum covered with smoked paper and revolving by clock-work with a 

 definite velocity. The point of the lever writing upon the paper produces 

 a tracing of the heart's impulse or cardiogram. 



Endocardiac Pressure. The effect of the muscular contractions 

 and relaxations of the walls of the heart during its systole and diastole is to 



FIG. 158. Double Cardiac Sound for Simultaneous Registration of the Blood Pressure in the 

 Right Auricle and Ventricle, or in the Aorta and Left Ventricle. (Hiirthle.) 



produce varying changes of pressure on its content of blood. When this 

 pressure is measured by the proper instrument it is found that the pressure 

 in the left ventricle varies between wide ranges. With the beginning of 

 the muscular contraction, the pressure rises till it slightly exceeds that of 

 the pressure of the aorta, remains high for a brief interval of time, then slowly 

 and quietly decreases to less than that of atmospheric pressure and remains 

 low until the beginning of the next systole. For the right ventricle the events 

 and variations are relatively the same. 



