. The science and practice of medicine . noris it probable he ever heard of Dr. Learedsstethoscope. He never called it Cammans Double Stethoscope; this was done bythe instrument-maker. It has been said that he did not appreciate the value of his own instrument, pos-sibly because he did not assert his claim to its originality, and from the fact that afterthefirst year of its introduction he used it sparingly, finding that its constant appli-cation to the ear sensibly dulled the delicate acuteness of hearing so prized by theexpert. To understand the rationale of this effect, it is well to premis
. The science and practice of medicine . noris it probable he ever heard of Dr. Learedsstethoscope. He never called it Cammans Double Stethoscope; this was done bythe instrument-maker. It has been said that he did not appreciate the value of his own instrument, pos-sibly because he did not assert his claim to its originality, and from the fact that afterthefirst year of its introduction he used it sparingly, finding that its constant appli-cation to the ear sensibly dulled the delicate acuteness of hearing so prized by theexpert. To understand the rationale of this effect, it is well to premise that the doublestethoscope conveys the same sound-impression through a distinct channel to each ear,just as the stereoscope presents an individual picture of the same object to each eye;and the. effect in each case is to produce in the brain a clearer perception of the en-tirety of the sound heard or the object seen, than can be done by one ear or one eyealone; but no instrument can do this perfectly unless both ears or both eyes are. 1 Self-adjusting Bin-aural Stethoscope of Dr. Camman. EXAMINATION OP THE CHEST IN AUSCULTATION. 549 Another form of double stethoscope has been devised by Dr. ScottAlison, and named by him the differential stethoscope. LikeDr. Leareds instrument, it has a tube for each ear; but each tubehas a separate cylinder or cup, which admits of being applied to anypart of the chest. Dr. Leareds instrument enables us to hearsounds emanating from any given portion of the chest with bothears simultaneously ; while Dr. S. Alisons instrument enables usto listen to the sounds emanating from two different parts of thechest at the same moment, so that we may compare the sounds atany two points, or on opposite sides of the chest, by a series of con-secutive observations. If two sounds exist, one at each point, andif they differ in intensit}r, the weaker sound is eclipsed or nullified. All forms of stethoscope require much practical study and ex-perience to use them
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