Laennec discovered "mediate" auscultation in 1816 while examining a female patient whose stoutness made "direct" auscultation-where the physician placed his ear on the chest of the patient-impractical. Taking a piece of stiff paper, Laennec rolled it into a tube and placed one end on the patient's chest and the other against his ear. He had inadvertently invented the stethoscope.

This first edition of Laennec's De l'Auscultation Médiate [On Mediate Auscultation] depicts his stethoscope after three years of experimentation. A wooden tube about 30 centimeters long and about 6.75 millimeters in diameter, the instrument was constructed in two pieces that could be unscrewed for easier portability. Readers could purchase the instrument directly from publisher at first, but the simplicity of the design allowed it to be replicated by any competent woodworker.