PERCUSSION, in medicine, is the method of eliciting sounds by striking the surface of the body, for the purpose of determining the condition of the organs subjacent to the parts struck.
This means of diagnosis was first employed by Avenbrugger in the middle of the last century ; it was afterwards extensively adopted by Corvisart in investigating the diseases of the heart, but its value, like that of all the other branches of auscultation, was not fully appreciated till Laennec made them the subject of his peculiar study. Since his time, its value has been considerably enhanced by the labours of M. Piorry.
Everybody knows that when a hollow body is struck, there is a vibration produced in the air within it, which being communicated through the walls to the external air, produces a ringing Pound, whose tone varies with the size of the hollow body, the material of which it is composed, and many other circumstances ; hut that if the same body be filled with a fluid or a nearly solid substance, no other sound is produced than that which results from the striking together of two solid bodies of the same materials as the wall of the cavity and the substance with which it is struck. On these circumstances the practice of percussion is based. If any part of the body beneath which there is a hollow organ, or one containing air in tubes, bo struck, a resonance is produced ; if any part which lies over a solid or a fluid be similarly struck, the sound emitted is merely the dull noise of two solid and rather soft bodies.
The modes of employing percussion are various. The simplest and most convenient is to place one finger of the left hand flat upon the part to be examined, and to strike it lightly, but rather sharply, with the ends of the three first finger!' of the right hand set close together on the same level. Instruments called plexlmetera have been Invented by M. Piorry and others: they are composed of small plates of cork, india-rubber, light wood, or ivory, which being held by their edges or by a handle, are placed on the part to be examined, and struck with the fingers, or with a small hammer. Whether the hammer and plexi meter or the fingers are used, care should be taken that the blows are always given with the same or an exactly estimated degree of force, and that they should fall perpendicularly to the surface of the organ to be examined.
Percussion is chiefly employed in the diagnosis of diseases of the lungs, heart, and abdominal organs. [PIITHISIS; HEART, DISEASES OF, &C.] The lungs being chiefly composed of tubes and cells filled with air, there is a certain degree of resonance when the chest over any part of them is struck; but the character of the sound varies somewhat both in intensity and in tone, according to the part of the cheat examined, and the thickness and softness or hardness of its walls : in all parts however, when the luogs are healthy, there is resonance. When
however the lung is covered by fluid, or has the quantity of air in it lessened by obstruction of the air-tubes, or by deposits of fluid or solid substances in or aronnd the cells, the resonance of the chest directly over the part affected is diminished or entirely lost, and in extreme cases the only sound obtained by percussion is the dull sound of the contact of the fingers with the wall of the chest. When, on the other hand, the air-cells are dilated, and the lungs contain a greater pro portion of air than is natural to them, as in emphysema of the lungs, the resonance of the chest is in a corresponding degree increased. The various degrees between perfect dullness, such as occurs when the lung is covered by fluid [HynaosnosAx], or rendered solid by inflammation [LUNGS, DISEASES or], or by tubercular deposition [Prrarsis], and the highest degree of resonance in emphysema are numerous, but are of course appreciable only by a very practised ear and hand. To them the evidence they afford is scarcely less valuable than that obtained from the use of the stethoscope, with which the practice of percussion should, in all diseases of the chest, go hand in hand.
In the healthy state, the chest, when struck over the region of the heart, emits a duller sound than that which proceeds from the rest of its walls. In the natural size of the heart this region occupies a space of an inch and a half or two inches square, situated just to the left of the sternum, at the level of the fourth and sixth ribs. When either the heart itself is enlarged, or a quantity of fluid is accumulated in the pericardium, the extent of this less resonant region is increased in a corresponding degree ; but the changes of sound which it emits depend greatly on the coincident condition of the lungs, and the extent to which their anterior margins overlap the front of the heart.
By percussion on the abdomen one may obtain information, approxi mating to truth, of the size of all the solid organs, by the extent of the dullness of sound in their respective regions ; and of the degrees of inflation, and even of the nature of the contents of the digestive canal and the peritoneal cavity, whether solid, liquid, or ariform; but the evidence thus obtained is on the whole leas definite in the diseases of the abdominal organs than in those of the heart and lungs.
(31. Piorry, De la Percussion mediate, Paris, 1828 ; Bennett, Intro duction to the Study of Clinical Medicine,1860 ; Weber, On Auscultation and Percussion, translated by Cockle, 1854 )