THE CIRCULATION 



115 



5. Intracardiac Pressure. Expose the right external jugular vein. 

 Place a clip upon it centrally and ligate it about 2 cm. farther distally. 

 Open this vein between the clip and the ligature and insert the end of a 

 long, hollow probe filled with physiologic salt solution. Place a liga- 

 ture rather loosely around that portion of the vein which contains the 

 end of the catheter. Connect the latter with a membrane manometer. 

 Remove the clip from the vein and push the catheter slowly downward 

 until its free end comes to lie in the right auricular cavity. Obtain a 

 tracing of the right intra-auricular pressure. 



Push the catheter through the auriculoventricular orifice into the 

 right ventricle, taking care not to injure the tricuspid valve. Obtain 

 a tracing of the right intraventricular pressure. Withdraw the catheter 

 and replace the clip upon the vein. 



FIG. 74. DIAGRAM OF MEMBRANE MANOMETER. 



M, Rubber membrane connected with writing lever (L). The drum (T) is connected with 

 the cannula in the blood-vessel; R, rod to fasten manometer to stand. 



Study the character of each tracing and compare them with one 

 another. Calculate the pressures so obtained by comparing the oscilla- 

 tions of the membrane with those of a mercury manometer. 



6. Entrance of Air Into the Circulation. Insert a glass cannula in 

 the right external jugular vein. Record the blood-pressure, and apply 

 a stethoscope to the chest wall. Force a small amount of air into the 

 aforesaid vein. After a short latent period the blood-pressure will begin 

 to fall, this fall being accompanied by a peculiar noise produced by the 

 frothing of the blood within the heart, as the valve flaps beat against 

 the bubbles of air. 



Kill the animal by an overdose of ether. Open the heart and ex- 

 amine the character of the blood. Dissect the heart, repeating the 

 observations made in the course of Lesson XV. 



