548 



BELL SYSTEM TECHNICAL JOURNAL 



650 cycle filter and the second with a band pass 130-1,100 c\cle filter 

 and increased amplification. The latter shows the s\'stolic niurnuir 

 very clcarK'. With ilic LP (JoO filter, the nuirnuir is more or less 

 obscured li\ siry Inw pitched sounds wliicli nia\ really be a part 



E 



Low pass 650 cycle filter 



Band pass 1,?0-1100 cycle filter 



Fig. II — Kecords of a systolic imirimir taken with the stethoplionc and a recording 

 galvanometer 



of it, 1)111 cerlaiiily pla\- a suliordiiiaic role in pnidiicin.u llu' .uidilik' 

 sDtuid. Tile clU'ct ot siippri'ssiini tiii' low pitched sounds 1)\- using 

 lln' iiigh p.iss tilti-r is mnw pronounci'd in charts of this sort for niur- 

 nuirs which lia\e negligilik' sotind coniponcnts below \'M) c\-cles 

 per second. 



Phonograph records of heail Mnuids ha\e been made i)re\ ioiisK." 

 With the stelh()|)hone and a special electrical recorder, records of 

 some 1") cases of murmurs and chest sounds ha\c recently been made. 

 The results are very encouraging. All nf ihc i haracteristics of these 

 sotmds, such as the relati\e intensities of liie dilTerenl components 



" (,. !•■. Keiper, Leller J. .1. .1/. .1., 81:679 .•\ug.^25, !')_',<. 



