536 BELL SVSTFM lECllSlCAL JOURSAL 



Iransmiltcr lo tiMchint; was due largel\' to the work of Dr. R. (". 

 ("alw)l and Dr. C. J. Cjainhle al tlic Massadiiiselts (ieneral Hospital 

 where a successful multiple electrical stethoscope was first employed 

 for classroom lectures in June, 1923. The equipment consisted of an 

 electromagnetic transmitter provided with a special form of mouth- 

 piece for picking up the body sounds, a three-stage vacuum tube 

 amplifier and a distribution system to accommodate as many as 

 125 students with single head receivers on which individual ordinary 

 stethoscopes were held.'- 



The e.xperience gained with liiis equipment indicated certain 

 improvements to increase the sensitivity to body sounds, and at the 

 same time decrease the disturbances caused by extraneous noises. 

 Greater sensitivity required a better transference of sound energy 

 from the body to the transmitter. Reduced room noise required that 

 we couple the transmitter as closely as possible with the human body 

 and at the same time make it insensititive to sound vibrations in the 

 air. A preliminary analysis with electrical filters of the frequency 

 characteristics of sounds of pathological interest to the physician 

 showed that these sounds were composed largely of frequencies below 

 1,000 cycles. Inasmuch as the frequency characteristics of these 

 various sounds are different, it has been found very useful to permit 

 concentration on the sounds of interest by the use of electrical filters. 



These factors led to the development of the electrical stethoscope 

 called the "stethophone" which is described in the following para- 

 graphs. This development was undertaken at the request and with 

 the active cooperation of Dr. H. B. Williams of the College of Physi- 

 cians and Surgeons, New York, Dr. Richard C. Cabot " of the Massa- 

 chusetts General Hospital, Boston, and Dr. C. J. Gamble'- of the 

 School of Medicine of the l^niversity of PennsyKania, Philadelphia. 

 The cooperation of these physicians permitted the instrument to be 

 gi\i-n i)ractical tests at e\ery stage of its de\clopnient. 



3. Gi:m:rai. Di;si kii'uon or tiik SniriiDriKiNK 



The stcthoiihone consists essentialK- of tlu' fullowinu ckMiioiits: 



1. An electromagnetic transmitter. 



2. A three-stage amplifier with a pnienlionieier control. 



3. .A selected group of electric filters. 



t. A multiplicity of output receivers for observers. 



The whole is assembled in a substantial cabinet on wlueis re- 



'■- A detailed desiriplion of the apparatus ii.scd In this installation was presented 

 in a recent palmer. See (".amble and Keploglc, ".\ Multiple Electric Stethosi-opc 

 for Teaching," J. A. M. A., Vol. 82, p. 387, 1924. 



