and the parietes of the chest. The amount of resonance, however, of the one side, may often, particularly in thin persons, be usefully compared with that of the other by rounding the shoulders, inclining the head forwards, and giving a firm strong stroke. The Inter-scapular regions are moderately resonant, excepting close to the spine, where the thick layer of muscles attached to the bony column prevents the sound being fairly brought out. By crossing the arms, and thus drawing outwards the scapulæ, and rendering the integuments tense, very tolerable resonance may, however, be generally elicited from these regions, excepting in very stout persons. The Infra-scapular regions are very resonant superiorly, but on the right side dull on strong percussion, and fairly sounding only upon gentle tapping below the eighth or ninth rib, in consequence of the upward projection of the liver, which in the natural condition affects the resonance in front considerably above the level at which it modifies it posteriorly. On the left side the Infra-scapular region may be rendered tympanitic by the stomach, or colon, distended with gas; or dull either from an unusual enlargement of the left lobe of the liver, or an hypertrophied spleen; but it is usually much more resonant inferiorly than the corresponding region of the opposite side.

The different regions, independently of any

disease in the chest, but influenced by the constantly varying condition of the hollow organs of the abdomen, may be arranged as follows, according to their amount of resonance.

Tympanitic, (occasionally,) from distension of the stomach, &c., the lower part of the left Mammary, left Lateral, and left Infra-scapular regions.

Very resonant.-The Superior Sternal, the Axillary, and the upper part of the Infra-scapular regions.

Resonant.-The Subclavian or Infra-clavicular, the upper part of the Mammary and Lateral, and the Inter-scapular regions, excepting the inner edge of the left Mammary.

Imperfectly resonant.-The Acromial and the lower part of the right Mammary, Lateral, and Infra-scapular regions.

Dull.-The Inferior Sternal, the inner edge of the Left Mammary, and the Scapular regions.

4. The indications afforded by Percussion. 1. In diseases of the Lungs and Bronchial Tubes.

As in simple Bronchitis there exists merely an increased supply of blood in, together with some thickening of, the lining membrane of the tubes, there is no appreciable alteration of the resonance of the chest. Natural resonance of the chest, therefore, is one of the signs of simple bronchitis. The consequences of the complaint, however, often modify the sound elicited by percussion. Thus, in the debilitated patient, pulmonary congestion,

particularly of the more dependent parts of the lung, may be a direct result; and this may exist to such an extent as to be accompanied by dulness on percussion. From the long continuance, or frequent repetition of bronchitis, emphysema arises, which is attended with increased resonance of the chest.

In the early stage of Pneumonia, the pulmonary tissue contains a larger supply of blood than in the natural condition, and the air-cells and intervening spaces are, at least, partially filled with serous fluid. The ordinary quantity of air, therefore, cannot gain admission to the interior of the cells, the elasticity of the tissue is decreased, and the resonance on percussion is consequently diminished. When, instead of being partially occupied by fluid, the air-cells are filled with solid or semi-solid matter, or are closed by the thickening of their walls, and the air is entirely excluded from their interior, as in the advanced stages of the complaint, when, in fact, hepatization is established, the dulness on percussion becomes much more marked, and the resistance afforded to the finger more decided. As, in the progress of cure, the engorgement of the pulmonary tissue decreases, and the cells become partially free, the amount of dulness, together with the resistance communicated to the finger, gradually diminishes.

When, on the contrary, pneumonia passes on to the third stage, and the effused matter softens down, though air may gain admission to the

disorganized tissue, the resonance on percussion does not increase in proportion: excepting in the comparatively rare case of large pneumonic abscess, variation in the amount of dulness is often scarcely perceptible. The comparatively slight change of the dulness in such cases probably arises from the contraction of the surrounding tissue, and simultaneous depression of the ribs, as well as from the commingling of purulent or softened albuminous matter with the inspired air.

Percussion, then, forms an important element in the physical diagnosis of pneumonia. It not merely assists the physician in ascertaining the existence of the disorder, but, when the case is carefully watched, it enables him to determine its stage and progress.

Is dulness on Percussion, then, always attendant upon pneumonia ?-It certainly is not. The disease may certainly be present without any appreciable dulness. Thus, when inflammation affects separate lobules of the lung, disseminated through one or both organs, and these lobules are surrounded by a comparatively large amount of healthy crepitant pulmonary tissue, no dulness can be discovered on percussion. It is from this form of the disorder being more frequent among children, as well as from physical examination being in them effected with less facility than in adults, and from the patients frequently dying before the disease has arrived at the stage

of consolidation, that the pneumonia of childhood is less commonly attended with dulness on percussion, than that of grown persons. There are other cases in which pneumonia cannot be recognized by dulness: as when a defined portion of hepatized lung occupies the centre of the organ, and is on every side surrounded by healthy structures, or when it exists in situations normally dull, as in the thin edge overlapping the heart, or in that passing down before the liver.*

In Phthisis the dulness on percussion is very variable. In some few cases it cannot be dis

covered during their entire course. Its importance, like that of almost every other physical sign in this complaint, is associated with the comparison of one part with another, or of corresponding regions in the two sides of the chest. Phthisis almost always primarily affects the apex of the lungs, and most commonly that of one before, or to a greater extent, than the other. Upon this circumstance do the distinctive physical signs of the complaint mainly depend. When, therefore, tubercles are largely and equally distributed throughout the whole of one or both

* It has been stated, upon high authority, that in some cases of consolidation of the lung, the side has been more resonant than natural, and even tympanitic, upon percussion. This curious circumstance has been differently accounted for by different writers, but as the author has never witnessed such a case, the exception has not been introduced in the text.