Wm. J. Kerr 



271 



In coarctation of the aorta a systolic murmur frequently is heard over the 

 upper thoracic spine and between this area and the left scapula. If one chest 

 piece of the symballophone is placed over the apex and the other over the 

 area in which the murmur is heard, it will be readily noted that the murmur 

 appears appreciably later than the first or systolic sound at the apex. The 

 reasons are that the area of coarctation usually is found in the descending limb 

 of the thoracic aorta and that the pulse wave arrives in the aorta at that point 

 about 0.05 sec. after the systolic contraction of the heart. Arteriovenous aneu- 

 rysms in the orbit, cranium, and extremities lend themselves to more accurate 

 study with the symballophone than with the ordinary stethoscopes. Blood- 



Foelal loGs-plpa^e: 160 per^ minute, IGbeais per^ Gseconda. 



Yoelal he3.v\ rale: ]60ipev minu-ie, UlDeais pep Gseconds. 



Fig. 10. Schematic representation of the auditory effects produced by two rhythmic sounds 

 of different rates as heard over the symballophone. When the rates are almost identical they 

 may be easily differentiated by the cyclic return of synchronous and asynchronous phases. 

 Foetal heart sounds in twin pregnancy in which the heart of each foetus has its own cardiac 

 rate may be taken as a clinical example. The foetal and maternal cardiac rates may be simi- 

 larly compared. 



pressure measurements by the auscultatory method may be made by applying 

 either chest piece of the symballophone over the artery distal to the point of 

 compression. 



With the symballophone foetal heart sounds may be compared with mater- 

 nal heart sounds. Such observations are of importance when the maternal 

 cardiac rate is high and the question of a viable foetus arises. Differences of 

 a single heartbeat per minute may be readily detected. Twin pregnancies may 

 be diagnosed if the two chest pieces are placed over the areas in which distinct 

 foetal sounds are heard. As the physician listens to the sounds, he will observe 

 that at times the two sounds are asynchronous, then they gradually approach 

 each other and finally they coincide. Thereafter they gradually move apart and 

 again approach each other in the next cycle, as shown in figure 10. Unless this 

 pattern of sound is kept in mind, the obstetrician will not be able to make an 

 accurate comparison when there is little difference in the foetal heart rates. 



Vocal Cords. Vibrations of the vocal cords produce a variety of sounds 

 through variations in length and in tension of the membranes. If one of the 

 paired cords is diseased or contracts imperfectly because of weakness of the 

 controlling muscles, abnormal vocal sounds are produced. In clinical medi- 

 cine it frequently is important to know whether hoarseness is due to local 

 disease or to paralysis of the muscles of phonation. If the physician stands 

 directly behind the patient and applies the chest pieces of the symballophone 



