Wm. J. Kerr 267 



differences in volume of the pulmonary tissue through which air is moving on 

 the two sides, which are determined by the position of the aorta. The ascend- 

 ing aorta encroaches on the right lung ventrad and the descending aorta on 

 the left lung dorsad. 



By the use of the symballophone, areas of consolidation, collections of fluid 

 or air, and other clinical conditions can be localized more accurately than by 

 any other auscultatory method. Medical students and physicians alike have 

 little difficulty in locating areas of abnormality in the chest because the device 

 makes use of the normal functions of the ears for the comparison and laterali- 

 zation of sound. The physician need not understand the details of construc- 

 tion.* He becomes concerned with the explanation of the causes for the dif- 

 ferences he observes in the areas of the chest. However, he must give some 

 thought to the functions of the membranes and the airways of the lungs in 

 which the sounds are produced if he is to interpret the significance of the 

 abnormal sounds he hears. 



Heart and Blood Vessels. In early life the closure of the semilunar valves is 

 accompanied by a sound which is of greater intensity or louder in the second 

 left than in the right intercostal space equidistant from and adjacent to the 

 costal margin. During and beyond middle life the intensity of the sounds over 

 these two areas is reversed. In the first instance we say that the pulmonary 

 closure (second) sound exceeds or is greater than the aortic closure (second) 

 sound, and in the second instance, that the aortic closure (second) sound ex- 

 ceeds or is greater than the pulmonary closure (second) sound. Many physi- 

 cians carelessly place the single chest piece of a binaural stethoscope over the 

 right and left second or third intercostal spaces and merely record the relative 

 intensity of the second sounds. With the symballophone the classical differ- 

 ences in the second intercostal space can be readily demonstrated. In the third 

 intercostal spaces the second sounds over the pulmonary valve are almost 

 always louder than over the aortic valve even when aortic hypertension exists. 

 A great increase in the pulmonary second sound is observed in patients who 

 have the clinical condition known as cor pulmonale. 



The second or closure sounds of the semilunar valves can readily be com- 

 pared in intensity with the first or systolic sound heard at the apex which 

 accompanies contraction of the ventricles. In myocardial failure this systolic 

 sound at the apex frequently is diminished in intensity although it may be 

 heard faintly in other conditions such as ptilmonary emphysema, pleural effu- 

 sion, pneumothorax, or pericardial disease with an accumulation of fluid or 

 air in the pericardium. 



Murmurs that arise in connection with defects in the valves travel with the 

 pulse wave. Diastolic murmurs are not propagated beyond the heart since 

 they are associated with the flow of blood into the cardiac chambers. Systolic 

 murmurs that arise in the heart, however, are of two types and may be de- 



* An analogous situation exists when a person with normal stereoscopic vision uses Oliver 

 Wendell Holmes's stereoscope. He perceives a sensation of depth without being required 

 to know how the device is constructed. 



