Wm. J. Kerr 261 



in detecting differences in quality of sounds and in lateralizing them through 

 differences in timing, intensity, and other less important factors. When the 

 hearing in one ear is defective, the ability to lateralize extraneous sounds may 

 not be lost entirely if any sounds can be heard by the affected ear, since the 

 ability to detect differences in timing may be retained. 



The stethoscope first described by Laennec in 1819 still is used by many 

 European physicians. It consisted of a hollow wooden tube for mediate auscul- 

 tation. It was interposed between the ear of the physician and the body of the 



Fig. 2. A simple device to demonstrate the remarkablv sensitive capacity of the ears to de- 

 tect differences of time of 0.000003 {one three-millionth) sec. consists of a rigid hollow tube 

 connected by rubber tubing of equal length and bore with the familiar headset of a stetho- 

 scope. Apertures are made in the hollow tube at the central point C and at points R^ and L^ 

 5 mm. to the right and to the left of the central aperture. Other apertures may be made at 

 any points R- and L- and R^ and L'' to the right and left of the central aperture. To test the 

 lateralizing sensitivity of the two ears through function of timing, sounds are made directly 

 over one of the apertines. When the normal subject listens while sounds are produced over 

 the central aperture, he hears the sounds simultaneously in both ears; hence there is no 

 lateralizing effect. When sounds are produced over apertures R^ or L'^ they will appear to 

 arise at points to the right or left of the midline. Since these points are only 5 mm. removed 

 from the center and the difference in distance to the two ears is 10 mm. or 1 cm., it is demon- 

 strated that differences of 0.000003 sec. can be detected. If sound waves in air travel at the 

 rate of 330 m. (i,o8o ft.) per sec, they \\ould travel 1 cm. in 0.000003 ^^c. Sounds that enter the 

 device at points R^ and L" and R" and L^ appear to arise at points progressively more remote 

 from the midline. The greatest differences in distance from the point of origin of sound to 

 the two ears necessary to give complete lateralization would be about 15 to 18 cm., or one- 

 fourth the circumference of the head. 



patient, and enhanced the accuracy of observations of sounds produced in 

 the body, notably in the lungs and heart. Incidentally it protected as well the 

 sensibilities of both the patient and the physician. Williams, in 1829, devel- 

 oped the binaural stethoscope fitted with two earpieces and with two semi- 

 rigid tubes joined to a device for application to the body of the patient. This 



