AN IDEAL stethoscope should be able to deliver to the ears, without important loss or distortion, all audible physiological phenomena. These sounds normally fall in the acoustic range of 60-600 cycles per second, with some unimportant components of mitral diastolic murmurs below 60 and a few pulmonary rhonchi and rales as high as 1,000 cycles. Popular conceptions notwithstanding, no acoustic stethoscope amplifies or increases the original sounds. The very best ones transmit them to the examiner's ears with relatively few losses. Since its introduction by Laennec, in 1819, the stethoscope has undergone many alterations and refinements, and it now consists of a number of interdependent elements. There are one or more chest pieces—the collectors or accumulators of sounds—a binaural with spring and ear pieces, and connecting lengths of flexible tubing. The natural characteristics of these components have been investigated and can be summarized as follows: The accumulator, or chest