96 EXPERIMENTAL PHYSIOLOGY. 



wave of depression following c is marked x and is due to a fall of 

 pressure in the auricle. What causes this fall in pressure? 



The next point to determine is the end of the sphygmic period. 

 This is found by measuring from the alignment mark to line 5 of 

 the carotid or line 6 of the radial (less 1/10 sec.) and transferring 

 to the jugular tracing. The line will be found to fall on a small wave 

 on the upstroke of the depression. This wave is marked V and is 

 due to the sudden opening of the tricuspid valves. Sometimes 

 another small wave just precedes V. It corresponds to closure of 

 the semilunar valves. Listen to the heart sounds while recording 

 a tracing in order to determine this fact. 



In preparing your report of the experiment, draw in the intra- 

 auricular and intra-ventricular pressure curves in relationship to 

 the venous curve. 



C. Cardiograms. Apply the button of the special receiving 

 tambour to the apex beat and connect with a recording tambour. 

 Adjust the position and pressure of the button until a maximal 

 movement of the writing style of the recording tambour is obtained^ 

 Apply the writing point to a carefully levelled drum and with this 

 running at moderately high speed, take a tracing. There is often 

 difficulty in securing a satisfactory tracing, and it may be necessary 

 to try another subject. Breathing should be suspended for a few 

 moments while the tracing is being taken. 



To INTERPRET THE CURVE. Adjust another receiving tambour 

 to the radial or carotid pulse with both writing styles in the same 

 perpendicular, and following the other directions described under 

 "Venous Pulse", mark on the cardiogram: 

 - 1. The beginning of the sphygmic period, E (line 3). 



2. The end of the sphygmic period, E (line 5). 



3. The auricular wave (beginning of this wave is line 1; the 



end of it, line 2). 



4. The beginning of ventricular systole (difference between 2 



and 3 equals the presphygmic interval). 



5. The opening of auriculo-ventricular valves (lowest point in 



tracing; somewhat difficult to determine). 



When satisfactory tracings have been secured apply a stethoscope 

 to the apex beat and after accustoming your ear to the sounds, mark 

 as accurately as possible, by free hand, the position on the cardio- 



