"IHr. STETHOPHOSr.." ./.V El.V.CTRh'AI. STETHOSCOI'I: 547 



natiir.il cxeii witli idi-.il room conciilions. While a loiiil s|)faker lias 

 hi't'ii used under pro|H'r acoustic conditions to reproduce fainl 

 patliological sounds, as nnirnuirs and rales, this does not appear in 

 general to he a practical arranj^ement. Most arjjiunents, except per- 

 haps that of economy, tend to fa\()r the use of individual output 

 receivers for practically all purposes where critical anaKsis of sounds 

 is the objective. 



I-'etal heart sounds as heard throut;h the mother's alidomen are 

 nuich fainter and require considerably higher amplification than 

 adult heart sounds. Preliminary data indicate that the energy- of fetal 

 heart sounds is approximately only 1 50 to 1 500 of the energ\' of 

 average normal heart sounds. The low pass 130 cycle fdter is not 

 only useful for suppressing the extraneous sounds and electrical 

 disturbances which usually attend the use of high amplification, 

 but serves most effecli\ely to eliminate the voice sounds of the patient. 

 .-\t Sloane Hospital in Xew ^'ork City it has been found possible to 

 reproduce clearly on a loud speaker and with a negligible amount of 

 interference, fetal heart sounds which were barely audible in the 

 physician's stethoscope. In these cases no interference was exper- 

 ienced from the maternal heart sounds. However, even in surgical 

 work where the rate of the adult or fetal heart is alone of importance, 

 it is felt that the best plan is to equip an attendant with earpieces 

 attached to a recei\er and to make it his chief duty to ol)ser\e the 

 heart action. 



A ver\- important application of the electrical stethoscope is its 

 association with a recording galvanometer for making photographic 

 records of heart and chest sounds. Permanent records of this sort 

 might constitute a valuable addition to the history records of im- 

 portant cases in large hospitals. Some excellent graphical records 

 have already been made.'" It has been found that such records 

 can he obtained much more easiU' with the stethophone, principalK- 

 liecause of the part played by the electrical filters. The low-pass 

 filter suppresses largely the current fluctuations caused by mechanical 

 \ibrations and noise at the apparatus. The high-pass 130-c\cle 

 filter is also valuable for bringing out very faint murmurs. By its 

 use, the amplitude of the normal heart sounds can be greath' reduced. 

 When this is done, the amplitude of the faint murmur sounds may be 

 m.ignified relatively and hence shown very nicely on the record. 



This is illustrated in the two charts c.f I'ig. 11, which are presented 

 through the courtesy of Dr. H. B. \\'illiams. The stethophone 

 records are accompanied by simultaneous electro-cardiograms (Kl 

 for timing the events. The first record was made with a low pass 



