CIRCULATION OF THE BLOOD. 



Make a series of rapid shallow respirations. Is there any change 

 in the tracing ? 



Make a series of deep slow respirations. What change occurs 

 in the tracing ? 



Hold the breath for fifteen seconds. Note any change in the 

 volume tracing. 



While the tracing is being taken, work out some mathematical 

 problem. What is the effect on the volume of the arm ? 



Immerse th free hand in ice water. This will cause a primary 

 vaso-constriction in the vessels of the hand. Is there a corre- 

 sponding vaso-constriction in the other hand, as indicated by a fall 

 in volume ? 



Allow the subject of the experiment to take a few whiffs of amyl 

 nitrite. This is a general vaso-dilatant. What is the effect on the 

 plethysmographic tracing ? 



APEX BEAT, CARDIOGRAM, AND HEART SOUNDS. 



1. Let a student strip to the waist. Locate the apex impulse. 

 What is its relation to the sternum? to the nipple? to the ribs 

 and intercostal spaces ? How does its position vary with the posi- 

 tion of the subject ? 



2. Map out the cardiac area on the chest wall (a) with light 

 percussion; (b) with heavy percussion. Mark the area on the 

 chest with a colored pencil. 



3. Prepare a cardiograph as follows: Take a large thistle tube, 

 about five centimetres in diameter, stretch a rubber membrane 

 across the top and cement a cork button to the middle of the 

 membrane. Connect this, through a piece of pressure rubber 

 tubing, with a recording tambour whose diameter should be some- 

 what less than that of the thistle tube. In order to obtain 

 sufficient magnification, the recording lever should be about 

 twenty-five centimetres long. A good writing point may be cut 

 out of a piece of the glazed paper used for tracings. . 



Adjust the writing point of the recording lever to the smoked 

 paper of a medium-slow drum. Press the button of the receiving 



[.09] 



