AETEEIAL MUBMUES. 277 



produced by the pressure of the end of the instrument on the 

 artery. The following is the mechanism of the production 

 of this sound : The pressure of the instrument produces a 

 constriction in the vessel, and more or loss obstruction to the 

 current of blood. As the blood flows from this constricted por- 

 tion into that just beyond, where of course the vessel is rela- 

 tively larger and the current is somewhat retarded, the rela- 

 tively small and forcible stream produces an unusual and 

 irregular current, which is accompanied by a certain sound. 

 It has been proven by the experiments of Chauveau and 

 Marey with elastic tubes, that this sound is always produced 

 when any part of the apparatus is dilated so that the fluid 

 passes from the tube into a sort of sac. In this way aneuris- 

 mal murmurs are accounted for. The sounds which are 

 heard in the arteries, and are not dependent upon compres- 

 sion with the stethoscope, depend upon conditions, the con- 

 sideration of which belongs to pathology. 



