262 



The Symballophone 



instrument was improved by Camman in 1855 and by Alison and many others 

 in subsequent years. In use the original Laennec stethoscope was clumsy and 

 the sounds heard through it appeared to arise directly in the ear. The binaural 

 stethoscope constructed with connecting tubes of equal length and bore pro- 

 jected the sound by illusion to a point directly in front of the physician. He in- 

 stinctively turned his head toward the point to which the chest piece had been 

 applied in order to ascertain the location of certain sounds. In making studies 



of homologous areas on the surface of the 

 body, he had to move the chest piece between 

 the two points to be compared. He could 

 compare the qualities of different sounds 

 but he could not perceive the finer variations. 

 By this auscultatory method differences in 

 timing of events in two areas that produced 

 sound could not be detected, although when 

 it was combined with palpation the move- 

 ments of the thoracic cage and the events in 

 the cardiac cycle could be correlated in some 

 measure with the auditory evidence of mo- 

 tion at nearby or remote points. 



During the century since the invention of 

 the stethoscope, many improvements have 

 been made in the chest pieces. Multiple 

 stethoscopes have been devised that permit 

 several auditors to listen simultaneously to 

 a given sound. Audio-amplification has been 

 adapted for use in large halls or by special wiring of individual receivers at- 

 tached to the ordinary binaural stethoscope. A system of electrical filters has 

 been introduced to peirnit study of the bands of frequency of sounds pro- 

 duced in the body. In recent years several types of double stethoscopes have 

 been described. Muralt^ in 1910 devised a stethoscope which permitted the 

 physician to listen simultaneously to two areas over the lungs. This double 

 stethoscope consisted of two chest pieces or acoustic bells each of which could 

 be connected to one ear by a rubber tube. It is apparent from his illustrations 

 that the length of the crossed tubes to the opposite ears was equal to that of 

 the tubes passing directly from a chest piece to the ear on the same side. Sounds 

 originating in either chest piece reached both ears simultaneously. More re- 

 cently Froschels" suggested the use of a "differential stethoscope," which is 

 essentially a pair of chest pieces connected to the ears by an X- (or four-way) 

 connection to permit either an ipsolateral or a contralateral course of the 

 sound to each ear. This instrument was devised to study the sounds produced 

 in the vocal cords during phonation in cases of paralysis of the laryngeal 

 nerves. Nicolai^ devised a "stereostethoscope" to observe differences in sounds 

 originating in the two tempero-mandibular joints, and suggested its use in 



Fig. 3. Arrangement of the three 

 trumpets described in the text. 



