1808: The introduction of chest percussion

Prior to the 19th century diagnosis of lung disease was made by patient complaint and physician assessment without any tools.  By the 1850s physicians had access to to the technique of chest percussion.

Chest percussion being performed

Chest percussion is a method still used by today's physicians.  It's a technique that involves tapping on the chest and listening to the sounds emitted.  Different disease states emit different sounds, such as tapping over the heart produces a dull sound, and tapping over an area of the lung filled with fluid -- as in pneumonia -- also produces a dull sound.

Percussion is Latin for to beat or to strike, and may have originally been used to describe the beating or striking of the first man-made instruments.  Erik Soiferman and Eric Rackow in their article, "A brief history of the practice of percussion," wrote that the technique of using percussion to diagnose diseases was used as far back as the 17th century B.C. in Ancient Egypt. (1)

Joseph Auenbrugger (1722-1807)

Yet it wasn't until Joseph Leopold Auenbrugger (1722-1807) in a book he published in 1761, that percussion was identified as an official medical technique for doctors to use.  Soiferman and Rackow describe how Auenbrugger gave credit for his discovery to his father who would tap on kegs to determine how full they were.

The Catholic Encyclopedia notes that Auenbrugger was born in 1722 to a hotel keeper who made sure his son received a good education at the University of Vienna.  At the age of 22 he became a physician at the Spanish Military Hospital where he worked for 10 years.  It was here he spent doing "observational and experimental studies (that) enabled him to discover that by tapping on the chest with the finger much important information with regard to diseased conditions within the chest might be obtained." (2)

Changes from the normal sounds by percussion of the chest he related to a certain condition of the lungs.  For example, fluid in one area of the lung such as pneumonia produced a dull sound.  He then would confirm his new diagnosis with autopsies he performed.  (3)

He also at one point inserted fluid into the lung of a corpse and then tapped on the chest to confirm if a dull sound was heard over the area the fluid was entered.  His studies confirmed his findings.  Erik Soiferman and Eric Rackow wrote that Auenbrugger "referred to these 'percussed' sounds as either high pitched, muted or dull." (4)

Jean Nicolas Corvisart (1755-1821)

Like with any new medical discovery Auenbrugger's discovery of percussion was rejected by the medical community.   It was rejected until a man named Jean Nicholas Corvisart came along. 

Jean Nicolas Corvisant: (1755-1821) became the first professor of medicine at the Charite Hospital in Paris, and it was here he studied the works of Auenbrugger and found the technique of percussion useful in diagnosing his own patients.

Corvisart championed for percussion in his 1808 book, "Inventum novum ex percussione thoracis humani," and while he didn't have to, he gave credit for the discovery to Auenbrugger.

Corvisart used the technique himself to help diagnose patients with tuberculosis.  Based on the sounds emitted he would be able to tell how large or small the tubercles inside a patient were, along with their locations. (5)

Corvisart and his students -- one of whom was Rene Laennec -- were believed to be the only physicians in the world who used percussion. Perhaps this was because Corvisart was among the few physicians who studied Auenbrugger's work. 
The technique may not even have been adapted by the medical profession if not for Napolean Bonaparte selecting Corvisart as his own personal physician.  (6)

Napolean was impressed that Corvisart used a scientific technique instead of simply guessing what was wrong, as his previous physicians had done. (a century.  (7)  Corvisart later championed Auenbrugger's technique in his 1808 book  "Inventum novum ex percussione thoracis humani."  While he didn't have to, he gave credit for the discovery to Auenbrugger.

Thanks to the writings of Corisart, and later Laennec, Auenbrugger's discovery would become readily accepted shortly after his death in 1807, and Auenbrugger would eventually go down as one of the great minds in medical history.

References:

1.  Soiferman, Erik and Eric Rackow, "A brief history of the practice of percussion," http://www.antiquemed.com/percus.html
2. "The Catholic Encyclopedia, "Leopold Auenbrugger," http://www.newadvent.org/cathen/02072a.htm
3. ibid
4. ibid
5. ibid
6. Williams, Henry Smith, "The Century's Progress in Scientific Medicine," Harper's Magazine, 1899, page 38
7. Unknown reference at this time.  I'll get it up soon