Wm. J. Kerr 



263 





other fields of clinical medicine. This instrument consisted of two chest pieces 

 connected by two separate rubber tubes to their respective earpieces. Hantsch- 

 mann and Nicolai' reported that this instrument was of value in the study of 

 cardiac and pulmonary disease. In 1935 Hawthorne^ described a differential 

 (double) stethoscope similar to that devised by Nicolai. Alison" had described 

 this type of instrument in 1858 and had given a report on its use in 1859. 



My personal interest in the possible value of a comparing stethoscope was 

 aroused in 1936 when before a meeting of the journal club of the Division of 

 Medicine one of my colleagues, 

 Dr. T. L. Althausen, gave a re- 

 port on Nicolai's paper.* Dur- 

 ing the discussion I pointed 

 out that, in nature, sounds 

 which are lateralized or com- 

 pared are heard in both ears 

 and that differences in timing 

 and intensity are factors which 

 aid in locating and comparing 

 sounds. In Nicolai's instru- 

 ment the sounds to be com- 

 pared could not be heard in 

 both ears under the conditions 

 existing in nature. During the 

 afternoon following this dis- 

 cussion, rubber tubing, four Y- 

 pieces, two similar chest pieces, 

 and a headset from an ordi- 

 nary binaural stethoscope were 

 assembled into a clumsy but 

 working model of the symbal- 

 lophone. The crossed tubes 

 passing from the two chest 

 pieces to the contralateral ears 

 were made longer than the di- 

 rect tubes, that is, those passing 

 from the chest pieces to the ipsolateral ears. Subsequently the bore of the 

 crossed tubes was reduced^ (fig. 4). This crude working model was capable 

 of giving information not readily obtainable by the binaural stethoscope.* 

 Homologovis areas in the two lungs could be compared by a method that 

 employed the normal functions of the ears for comparing sounds. Sounds 

 produced in the circulatory system by contraction of the heart and by the 

 movements of the pulse wave could be readily compared. In disease, mur- 

 murs propagated on the pulse wave beyond the heart were heard as soinids 

 in motion, in contrast to the isolated sounds heard with the binaural stetho- 



O O 



Fig. 4. (A) Nicolai's comparing stethoscope. (B) The 

 original symballophone showing the arrangement of 

 tubing. The diagonal tubes are longer than the lateral 

 tubes, and the bore of the crossed tubes is reduced. 

 The sounds to be compared are heard in both ears as 

 would be the case with sounds heard in nature. (C) A 

 possible variation of (B) but impractical because the 

 connections ^vould permit sound waves to pass freely 

 in either direction from the transverse connecting 

 tube. 



