The lungs lie in a cavity surrounded by the ribs and the diaphragm. When breathing in, the diaphragm is lowered and the rib-cage expanded. Air then flows into the lungs to take up the extra space. A number of chest diseases are caused by the accumulation of fluid. A fluid-filled cavity produces a dull thud. Percussion is thus a very quick way of detecting some chest disorders. The stethoscope is a very simple instrument but of great value to the doctor. It is merely a device for picking up sounds and vibrations (e.g. heartbeat) made by the body organs, and conveying these sounds to the ear. The modern instrument consists of a small funnel or a hollow drum attached to a forked rubber tube. Attached to the others ends of the fork are two ear-pieces through which the doctor listens when the cup is put on the surface of the body.
For many centuries ‘medical’ men had listened to the heart beating by direct application of the ear to the chest but this was unsatisfactory and certainly unhygienic. Rene Laennec is credited with inventing the stethoscope in 1816. The story is that the stoutness of his patient made it impossible for him to listen to the heart, and so, remembering some children playing with a hollow log, he rolled up some paper and used it as an ear trumpet. He was able to hear the heart more clearly than ever before. In 1819 Laennec published a book in which he described a wooden stethoscope he had constructed. The early stethoscopes were of this simple design, but soon the two-ear-piece models were developed. It is ironic that Laennec should have died of tuberculosis – one of the diseases that the stethoscope has done much to detect.
The stethoscope was first used in studying the heart and lungs, and this is still its commonest use. It is, however, frequently used for detecting the pulse in the arm, and also for investigating abnormalities in the elementary canal.
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