Percussion is a method of diagnosis which, as ordinarily employed, consists in placing the fingers of the left hand over the portion of the chest or other part of the body to be examined, and in percussing or lightly striking them with the tips of the fingers of the right hand, so as to elicit a sound. On applying this method, for example, to'the chest wall overlying the healthy lung a characteristic resonant percussion note is produced; if the chest wall overlying the heart is similarly examined, a dull sound results of quite a different character; while if the region overlying the stomach is percussed, what is known as a tympanitic sound is evoked. By the employment of percussion, certain diseased conditions of deeply-seated organs can be detected. For example, consolidation of the lung in pneumonia, and the presence of effusion in the pleural cavity in pleurisy, both yield altered percussion sounds. Again, the altered texture of the lung in phthisis is accompanied by an altered percussion note, and changes in the form and area of the cardiac dulness are met with in certain forms of heart disease. The method of percussion was discovered by Auenbrugger in the last century, and was greatly developed by Laennec; it is commonly employed in conjunction with the method of diagnosis known as auscultation (q.v.).