THE PHENOMENA NOTED DURING EACH CARDIAC CYCLE 293 



a tube through one of the pulmonary veins. The same procedures may- 

 be followed in the case of either ventricle. A pointed tube attached 

 to a manometer is forced slantingly through its wall. This method 

 does not entail a loss of blood, because the musculature closes firmly 

 around the tube. With the chest closed, the right auricle and ventricle 

 may be explored with the aid of a long catheter which is introduced 

 through the right external jugular vein (Fig. 148). A regurgitation of 

 the blood into the auricle does not result under these circumstances, be- 

 cause the tricuspid flaps close tightly around the tube. With the chest 

 intact, the left ventricle may be rendered accessible to the recording 

 instruments by means of a slender probe which is inserted through the 

 left carotid artery and the aorta. As holds true in the case of the 

 tricuspid valve, the semilunar flaps attach themselves firmly to the 

 tube so that a serious regurgitation cannot result. The chest remain- 

 ing closed, the left auricle is not accessible to manometric measure- 

 ments, but the pulsations of its wall may be registered by means of 

 a small rubber bulb which is advanced through the esophagus until it 

 reaches the level of this cavity. 



The Mercury Manometer. — The determination of the pressure 

 developed in the different compartments of the heart, may be effected 

 with the help of an indicator commonly designated as a manometer. 

 This instrument has been developed in two directions, its two forms 

 being known as the mercury manometer and the membrane manometer. 

 For the present we shall confine ourselves to a consideration of the 

 construction and method of application of the former instrument. 

 In its earliest form it consisted of a perfectly straight tube which was 

 filled with water, the pressure being indicated by the height of the 

 column of water. Later on U-shaped tubes were used as a matter of 

 convenience. A still more practical form was given to this instrument 

 in 1828 by Poiseuille, who displaced the water by mercury. As the 

 latter possesses a specific gravity 11.7 times greater than that of 

 blood and 13.55 times greater than that of water, the limbs of the U- 

 shaped glass tube could be materially shortened without diminishing 

 the range of this instrument. Another important modification con- 

 sisted in filling the connecting tube between the manometer and the 

 blood-vessel with an anticoagulating agent, for example, with a concen- 

 trated solution of sodium bicarbonate or magnesium sulphate. But, 

 when testing the pressures within the chambers of the heart, it is best 

 to use normal saline solution, because the leakage of even an inconsider- 

 able quantity of the aforesaid fluids into the circulation is prone to 

 produce undesirable results. To avoid this possibility Marey and 

 Chaveau employed a catheter, the free end of which was closed with 

 a delicate rubber membrane. 



The displacement of the column of mercury in the U-shaped tube may be read 

 off directly or may be recorded upon the paper of a kymograph in the manner 

 described by Ludwig (1847). A float of hard rubber is placed upon the mercury 

 in the distal limb of the manometer. The float in turn is equipped with a vertical 



