"TUF. STF.THOI'llOXn." .-/.V electrical stethoscope 549 



ami their quality, h.ivf Iniii retained remarkably well. The problem 

 i>f subsequent repriKluction of these records has i)een met satisfac- 

 torily in two ways, in both of which the factor of particular concern 

 is the elimination of "needle scratch" noises. First, an electromag- 

 iietic reproducer has Ix-en used in conjunction with the stethophone. 

 In this case, low-pass filters serve to reduce the scratching nf)ises. 

 Second, the records have been reproduced by attaching the ear- 

 pieces of the ordinar>- physician's stethoscope to a special adapter 

 used with a commercial phonograph reproducer. To reduce needle 

 scratch in this case it is only necessary to introduce some form of air 

 passiige between the reproducer and the binaural earpieces which acts 

 as a low-pass acoustic filter. The ordinary commercial phonograph 

 is quite unsatisfactory for reproducing these records partly for the 

 same reasons mentioned above relative to the use of loud speakers. 



Phonograph records of heart and chest sounds can be employed 

 to some extent for preliminan.- teaching purposes and do not recjuire 

 much equipment if reproduced acoustically. No patients are required 

 in this case, and the records can be accompanied by the analysis or 

 diagnosis of an expert. It is suggested that phonograph records 

 might be used to advantage as permanent records to follow the progress 

 of disease in important cases. 



11. StMXIARV 



A summary of the applications and limitations of a new form of 

 electrical stethoscope has been given. However, the extent of its 

 usefulness can be brought out only after it has been placed at the 

 disposal of experienced men in the medical profession. With it, 

 heart murmurs and rales can be magnified and observed with greater 

 clearness than with the ordinary stethoscope. Extremely faint 

 sounds may be heard clearly without great acuity of hearing by 

 inexperienced observers, a thing which has not hitherto been possible. 

 In several instances, murmurs have been disco\'ered with the stetho- 

 phone which were not discerned initially with the ordinary stetho- 

 scope although discernible after having heard them with the more 

 powerful apparatus. In a few of these cases, very faint murmurs, 

 although undoubtedly present could not be heard at all with the 

 ordinary stethoscope. It is felt that the electrical filters have played 

 an important part in such cases. These facts lead us to believe 

 that the stethophone may have real value for diagnosis. 



The field of physical research of body sounds has been touched 

 upon but lightly. For special purposes, an endless variety of elec- 

 trical fdters ran be used with the stethophone. 



