546 BELL SYSTEM TECHNICAL JOURNAL 



phone to the bedside. Long wires from the transmitter to the ampH- 

 fier cannot be tolerated on account of inductive disturbances from 

 neighboring telephone or other electrical circuits. If desirable, 

 announcements ma\' be made as before by talking close to the body 

 of ilu' patient under observation. In cases where exposure of a 

 Iiaiitnt is inad\isablc or where accurate statements pertaining to the 

 seriousness of a disease are preferably withheld from the patient, 

 announcements may be made by talking in a low tone of voice at 

 about one inch distance from the transmitter itself. Reasonably 

 satisfactory reproduction is obtained by this means. 



10. OniRR .Appi.ic.\tioxs 



.Aside from its application to teaching purposes, the stethophone 

 appears to have possibilities in fields which have not yet been thor- 

 oughly studied. Further experimental investigation by the medical 

 profession can alone bring out these possibilities. 



The possibility of substituting a loud speaker for the iiuiix idual 

 receivers in the output circuit has been investigated in a preliminar\' 

 manner. This problem invol\-es certain very fundamental factors 

 relating to the sense of hearing which must be considered carefully. 

 To a remarkable extent, the ear is capable of selective observation. 

 Ordinarily we listen to sounds through a sea of noise to which we 

 become so accustomed that we fail to notice it. However, when 

 listening to sounds near the threshold of audibility, such as the body 

 sounds under consideration, this noise may render the sounds of 

 interest inaudible. In order to hear them, it therefore, becomes neces- 

 sary to increase the loudness to a point well above that commonly 

 observed by the ph>'sician with his stethoscope. This increase in 

 loudness brings within the audible range, sound components ordi- 

 narily not heard and changes tiie quality of the whole as judged by 

 the ear. Such alteration of quality is obviously very unsatisfactory 

 for diagnosis or teaching purposes. Assuming that we had a\ailable 

 a perfect loud speaker, one that would transmit the very low and the 

 higher frequency components of faint body sounds without distortion, 

 difticulties would still be presented by the acoustic characteristics 

 of the room in which the loud speaker was placed. All rooms are 

 more or less reverberant. When these sounds are reproduced by a 

 good loud speaker in a small hea\ily damped sound-proof room, 

 they appear quite natural, but such a room is seldom available prac- 

 tically. None of the ordinary loud speakers with horns will transmit 

 ilic low lri'i|urn(ir> luTc of interest and would sound \i.t\- un- 



