Auscultation (Lat. auscultare, to listen), a branch of medical art by which the states and motions of internal organs are discerned through the sounds which they produce. Pulsations, respirations, and the vibratory movements in the body produce sounds which may be distinctly heard by placing the ear upon the walls of the chest, or other parts of the external frame. The heart beats strongly many times per minute, and each pulsation gives a shock to the surrounding parts, and also produces a double sound within the heart itself. At every breath the air is first drawn into the lungs, and again passes out by expiration. The passage of the air into the lungs produces one kind of sound peculiar to the act of inspiration, and its exit another peculiar to expiration. In a state of healthy action, the sounds of the heart and those of the lungs and air passages are of a peculiar nature, and a little practice enables the ear to become familiar with each special sound. In a diseased state, the action of both heart and lungs is modified to some extent, and the sounds produced are also modified in a peculiar manner.

To assist the ear in distinguishing these sounds, Laennec constructed the stethoscope (Gr.Auscultation 020064 , chest or breast, andAuscultation 020065 to examine), by the aid of which all the sounds of the heart and lungs may be distinctly heard, and the differences between healthy and diseased action readily discerned and classified. The art of auscultation has since then made rapid progress. - Auscultation is very useful in obstetrics, as well as in diseases of the heart and lungs. In difficult cases of parturition, it is often necessary to know whether the child is dead or alive in the womb before delivery. After the fifth month of pregnancy the pulsations of the foetal heart may be distinctly heard, and the "placental murmur,'1 caused by the uterine circulation of the blood, may also be distinguished by the ear. - Percussion is a branch of auscultation by which artificial sounds are obtained as a means of discerning the state of the parts from which these sounds proceed, particularly in regard to the presence or absence of air or liquids. - The art of auscultation is of comparatively recent date, but it was long believed to be a useful aid in diagnosis.

In the middle of the 17th century Hooke observed that "there may be a possibility of discovering the internal motions and actions of bodies by the sounds they make. ... I have been able to hear very plainly the beating of a man's heart." In 1761 Leopold Auenbrug-ger, a German physician residing at Vienna, published a small volume in Latin explaining an artificial method of producing sounds in various regions of the body, by which the physician might judge of the state of the subjacent parts. This method was percussion. The book remained almost unknown till 1808, when Oorvisart translated it into French, and made the method known to all the countries of Europe. The practice of percussion has since become general, and in many cases is found highly useful. The method of studying diseases from sounds made by percussion led to the method of observing sounds made naturally, by the action of the heart and lungs. Oorvisart took up the subject with great zeal, and three of his disciples, Double, Bayle, and Laennec, continued the same course, resulting in the discovery of the stethoscope, and the general use of auscultation.