Although stethoscopes have been used since the time of Laennec, little exact information concerning the efficiency of different types is available, and apparently most physicians are influenced in their choice of a stethoscope by exterior finish or by features which make the instrument easy to use or convenient to carry rather than by its inherent worth as an acoustic instrument. Many different end pieces of the chamber and bell type are in use, and, although it is unlikely that all of these are equally satisfactory, little information is available as to the acoustic properties of the different kinds. The same may be said of the different arrangements of tubing that are employed. The tubes, usually made of rubber, may be long or short and of large or small diameter, and they may consist of soft gum rubber or of much stiffer material; but again few data concerned with their acoustic