542 THE OUTGO OF ENERGY 



The first sound in comparison with the second 

 is of longer duration, lower pitch, and greater 

 intensity. The quality of the first sound is dull, 

 booming ; that of the second is sharp, valvular. 



4. With one finger feeling the cardiac impulse 

 observe the sounds with reference to systole and 

 diastole. 



The first sound will be found to be systolic, 

 i. e. it occurs with the contraction of the ventricle, 

 while the second sound is diastolic, being heard 

 at the beginning of ventricular relaxation. The 

 interval between the first and second sounds is 

 therefore very brief. The pause after the second 

 sound before the first is heard again, is consider- 

 ably longer. 



The first sound can be heard in the extirpated, 

 bloodless heart (dog). The contraction of the 

 ventricular muscle is therefore alone sufficient 

 for its production. But the sound is modified or 

 replaced by a murmur when the auriculo-ven- 

 tricular valves are sufficiently injured. It is 

 probable, therefore, that the sudden increase in 

 the tension of the auriculo- ventricular valves con- 

 tributes to its production. The second sound 

 obviously is due to the sudden increase in the 

 tension of the semilunar valves. It is replaced 

 by a murmur when these valves are rendered 

 incompetent. 



