Wm. J. Kerr 



265 



as well as by those experienced in the use of the symballojilionc. Differences 

 of 1 per cent in the flow through any two obstructing cylinders could be differ- 

 entiated by observing differences in intensity of the sounds produced. It was 

 almost impossible to arrange obstructions of equal bore, so that the smallest 

 differences in time could not be noted. However, by varying the bore and 

 length of the crossed sections of tubing, the differences in length and bore 

 which gave the most satisfactory results were obtained. When the crossed tubes 

 were approximately 15 cm. longer 

 than the direct tubes, the opti- 

 mal difference in timing to the 

 two ears was secured. When the 

 crossed tubes had an internal 

 diameter approximately three- 

 fourths that ol the direct tubes, 

 the differences in intensity of the 

 sound which reached the two ears 

 could be made to stipplement the 

 illusion of lateralization. 



A number of models with ex- 

 changeable metallic parts of vary- 

 ing length and bore were con- 

 structed. By practical experience 

 in normal and abnormal subjects, 

 it was found that the length and 

 bore of the tidies previously de- 

 scribed were the most satisfactory. 

 The final model" (fig. 6) differed 

 from model B shown in figure 4 

 in that the crossed and direct 

 tidies were made of rigid metal 

 tubing to insure permanency of 

 the essential functioning parts. The tubes from the chest pieces to the central 

 tmit were made of rubber tubing of equal length and bore to permit flexibility 

 in use. Rubber tubes of equal length and bore were inserted to connect the 

 central unit to the earpieces. Strong lateral steel-band springs were fixed to 

 exert equal pressure on the earpieces in the external auditory canals.* 



Clinical Observations 



Lungs. In examining the sounds produced in the lungs dining respiration 

 (auscultation), the physician who uses the ordinary binaural stethoscope usu- 

 ally moves the chest piece fiom one point to another in order to compare 



* The symballophone has been patented, and in order to protect it trom exploitation, tlie 

 rights under patent \o. 2,209,164 have been assigned to the Regents of the University of Cali- 

 fornia. The instrument is made and sold at or near cost with the iniderstanding that any 

 profit which may accrue from its manufactme and sale will be used for medical research. 



Fig. 6. The s)niballophone as finally constructed 

 al ter experimental and clinical studies. 



