LESSON XX 

 THE CIRCULATION (Continued) 



VENOUS VALVES. INFLUENCE OF DYSPNEA UPON THE BLOOD-PRESS- 

 URE. ACTION OF AMYL NITRITE AND ADRENALIN. HEMORRHAGE 



1. Position and Function of the Venous Valves. Ask the subject 

 to hold his arm in a dependent position. Encircle the forearm with a 

 piece of rubber tubing, but not too tightly. Raise the arm. Note 

 the distended condition of the veins upon the dorsal aspect of the 

 hand. Select the point of confluency of two veins. With the tip of 

 the index-finger of your left hand occlude one branch distally to this 

 point. With the tip of the index-finger of your right hand brush along 

 this vein in a direction from periphery to center, emptying the blood 

 into the collecting vein. Observe that the vein so emptied does not 

 fill again until you have removed the distal finger and have allowed a 



FIG. 70. RECORD OF THE CAROTID BLOOD-PRESSURE DURING DYSPNEA (Doo). 

 At L the tracheal tube was held shut until the blood-pressure began to drop. 



certain quantity of blood to flow into it from its tributaries. More- 

 over, while emptied a marked prominence is developed at its point of 

 confluency with the larger vein, indicating the position of the valve 

 guarding its central orifice. This experiment was employed by Harvey 

 to prove the circulation of the blood. Examine a preparation of a 

 segment of vein preserved in alcohol. 



2. Blood-pressure. Influence of Dyspnea. Anesthetize a mammal 

 and maintain the anesthesia until it has been killed. Perform trache- 

 otomy. Insert a cannula in the carotid artery and connect it with the 

 mercury manometer. Record the blood-pressure upon a slowly revolv- 



109 



