that there is no absolute normal standard, but merely relatively normal variations. In disease the sound side if such there be, must always be compared with the side which is diseased.

Selling has proved by means of resonators that the pulmonary note is a very complex one, made up of many overtones of which the lower ones predominate. The range of pitch of normal resonance is from low F to high C. In healthy adults it goes down to about low A; in children to middle F, in emphysema to low F. A dull note on the contrary is higher in pitch since the deeper tones are subdued through the decreasing vibratability of the lung.

The upper range of the pulmonary percussion note represents the pleximeter, the lower range is the lungs' own note. The latter varies with the amount of air and elasticity. The fact that the note between the large right and smaller left lung is not more noticeable, is probably due to the fact that when the note is low, a considerable difference in volume must occur before an appreciable change of the whole note is produced. When infiltration of lung tissue becomes complete we practically hear only the note of the pleximeter (finger).

In the lungs the pulmonary septa modify the sound by limitinglocalizing the sound waves; not, however, by acting at nodal points -they are too closely spaced-but by acting as a "load" on a vibrating string (see p. 55). If the lung is under normal tension, the vibrations remain localized in the area percussed. If it is relaxed, both lung and its contained air vibrate as a whole and tympany results.

Resonance occurs only over the lungs (elastic air-containing organs). The larger the quantity of air, the more resonant the note, especially if its deep diameter lies in the vertical plane of the percussion stroke.

Hyperresonance. By this term we understand a sound which acoustically lies between resonance and tympany, having some of the qualities of each but failing to be identical with either. It may be produced by percussing the normal chest during forced, deep, held inspiration (increased tension, and increased air), but is most characteristically heard in cases of pulmonary emphysema (increased air and diminished tension). The same concept may be expressed by "resonance with a tympanitic quality."

Dulness. A dull note is a short, high-pitched, non-musical sound. Percussion resonance disappears over the lung, and dulness takes its place as the result of the following physical conditions: (1) Absence of tone-producing material (consolidation of pneumonia, tuberculosis, infarction, atelectasis). (2) Poor tone conduction. (3) Poor conduction of the percussion stroke (exudation between the lung and the pleximeter-pleural thickening, effusions, edema of the skin). Dulness is "the sound of both fluids and solids, that of the airless viscera―liver, heart, spleen" (Da Costa).

Pulmonary dulness (lack of resonance) indicates an abnormally large proportion of solids or liquids in proportion to the amount of air in the pulmonary vesicles. With the appearance of dulness there is always an increase in the elevation of the pitch, and an increased sense of resistance. Acoustically, dulness is a condition in which the fundamental note preponderates, and but few overtones are heard.

A hand placed on a vibrating glass deadens the overtones. Its musical quality disappears, we hear only the fundamental note. Air-containing organs such as the intestines are more elastic, vibrate more readily and more complexly, furnish more overtones which produce a clearer, louder, longer, higher pitched, more intense and more musical sound (tympany). Solid organs on the other hand-liver, spleen, thigh-yield but few overtones, hence the sound is shorter, weaker and more muffled. Percussion of normal lung produces a larger wave amplitude-louder sound-than that of airless structures.

The dull note obtained by percussing pulmonary consolidation is characterized by the predominance of high-pitched sounds, those of lower pitch being weak or inaudible, and since high-pitched sounds fade out more rapidly than do low-pitched ones, the sound is not only high-pitched but also short, and does not carry far. The metallic, crackling râles heard in the neighborhood of pulmonary consolidation are even higher in pitch than the bronchial breathing which accompanies them (F. Mueller). The normal lung, under normal tension (inflation),

FIG. 59-Showing different degrees of percussion dulness in a case of pulmonary tuberculosis. The left upper lobe contains several cavities filled with blood clot and surrounded by consolidated lung, yields a very dull note. The right upper lobe is diffusely infiltrated, yields moderate dulness. The left lower lobe is slightly infiltrated and yields an "impaired" note. The right lower lobe is relatively free from disease and yields a resonant

note.

vields on percussion, a long, low-pitched, resonant, non-musical note. The pleximeter finger recognizes distinct elasticity (normal resistance). The breath sounds, except near the large bronchi or the trachea, are "vesicular "-soft, breezy and low in pitch. Expiration is much shorter than inspiration. Over the lower lobes the percussion note is longer and lower-pitched than over the upper lobes because of (1) the greater mass of lung tissue thrown into vibration; and (2) thinner overlying tissues. The liver on the right and the stomach on the left tend to add respectively a dull, and a tympanitic, quality to the lower pulmonary margin.

3

Impaired resonance or impairment is a term sometimes used to indicate slight dulness. It is somewhat shorter, high-pitched and less intense than resonance and is produced by the same causes, in lesser degree, which produce dulness-slight pulmonary infiltration, etc.

Flatness is a term which is applied to extreme or absolute dulness. The note of the thigh or of a fluid-pleural effusion-is flat. Some physicians prefer to use the expressions slight, marked and absolute dulness, to those just discussed. Efforts have been made to numerically classify or standardize different degrees of dulness as dulness number 1, 2, 3, 4.

Thus some examiners classify lack of resonance as 1-2-3-4-line dulness, using these terms to indicate respectively impaired resonance, dulness, marked dulness and flatness. This method of recording has not been satisfactory, owing to lack of standardization. The 3-line dulness of one examiner might be called 2- or 4-line dulness by another. It has been suggested1 that since these different degrees of dulness represent varying degrees of pitch, they might be standardized according to a musical scale, i.e.:

While such standardization would be most desirable, we cannot but question its feasibility especially among "non-musical" examiners.

MODIFIED TYMPANY

The tympanitic or musical sound already described sometimes undergoes certain modifications which give it distinct and separate qualities, producing what are known as (1) metallic ring; (2) bell tympany; (3) cracked pot sound. We have already learned that if vibrations are imparted to an air-containing cavity by a steady stroke applied to a large surface, rhythmic vibrations will be set up throughout the structure. If, on the other hand, a quick, sudden, localized blow be struck, the vibrations will tend to remain localized, will be unrhythmic and will produce a harsh, metallic, unpleasant sound. This may be illustrated by striking a piano string with a knife blade.

The conditions necessary for the production of markedly unrhythmic vibrations, and hence metallic sounds (a sudden localized blow, and a quick rebound) are most nearly fulfilled in the case of a large, tense, superficial cavity. Long before an explanation of the genesis of these sounds was forthcoming, Wintrich pointed out that metallic sounds could be more easily demonstrated by quick, forcible percussion, and when a hard, artificial pleximeter was employed. To produce metallic sounds we must have a stiff walled resonator which reflects better than it transmits. If the cavity is deeply situated, too much lateral radiation of the vibrations will occur before the cavity is reached, and vibrations instead of locally, will be set up generally, throughout it, producing a tympanitic note. If the cavity is small, the fundamental vibrations will be very rapid, and the overtones still more so. It is possible that a small cavity may actually yield a metallic sound which we merely appreciate as 1 WOOD, N. K.: "Percussion of the Lung." Jour. Amer. Med. Assn., Ixiii, 1914,

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tympany because the unharmonious overtones are above our auditory range (36,000 per second).

Metallic ring is a term which is applied to a percussion note having a metallic quality. It may be heard:

1. Over cavities not less than 4 cm. in diameter, with smooth, tense walls, especially if superficially located.

2. Over a tense pneumothorax.

3. Occasionally over intense apical infiltration. In this case, especially if right-sided, the trachea acts as the "large cavity with tense walls."

4. At times over a greatly distended stomach.

Metallic ring is best heard with staccato percussion and if stethoscopic auscultation be simultaneously practised.

Metallic ring occurs only over fairly large cavities because:

1. Small cavities vibrate too readily as a whole, and because their overtones are too rapid-high-pitched-to be perceptible.

2. Metallic ring is often associated with a short, high-pitched note which is closely allied to flatness.

Examples: Percussion of a thin tumbler yields tympany. Percussion of a thick bottle yields metallic ring. The fundamental note grows deeper as the size of the bottle is increased and its opening diminished. The metallic quality is especially noted if the ear be held near to the open mouth of the bottle (or of the patient in case of a patulous cavity). Percussion of a moderately inflated pig's bladder, the cheeks, or the stomach yields tympany; with extreme inflation the note becomes metallic.

Bell Tympany. Bell tympany is a clear, vibrant, metallic sound which may be heard by ausculting over tense pneumothoraces while percussion is practised on the opposite side of the lung, using silver coins as plexor and pleximeter. A clear-cut, slightly echoing sound is thus produced which has been likened to the sound of a gold coin dropped upon a marble slab, or the sound of a distant trolley bell. Acoustically the sound owes its character to the fact that sustained high-pitched overtones vibrate together with a deep fundamental note, and fade out slowly. Coins are used for percussion since being small, hard and metallic they tend to impart unrhythmic vibrations to the tissues beneath.

Cracked-pot Sound.-This is a metallic note, followed by a stenotic murmur, caused by the rapid expulsion of air, through a slit-like opening, as the result of the percussion blow.

"Though obviously related to metallic resonance, the nature and causation of cracked-pot sound are essentially different. The expulsion of air through a narrow opening plays a part in causing it. Apparently the edges of the opening are set in vibration, and an opportunity is thus given for the production of high overtones by interference" (Sahli).

Cracked-pot sound (bruit de pot fêlé) then is heard: (1) when air is forced through a stenotic opening as in the case of a superficial cavity communicating with a bronchus (vibrations of the tissues at the mouth of the cavity); (2) over the chest of a crying child (glottic vibrations); (3) occasionally over relaxed and infiltrated lung tissue. It is most marked if the examiner's ear be close to the patient's open mouth and during expiration. It is best heard over a superficial cavity near the pulmonary apex, with tense but resilient walls and a stenotic outlet. The sound

may be imitated by striking the loosely clasped hollowed palms of the hands together against the knee, or by suddenly percussing a perforated rubber ball. All metallic sounds are best elicited if forcible staccato percussion is employed.

Thus we find that: Rhythmic vibrations produce tympanitic sounds. Unrhythmic vibrations produce non-tympanitic

SUMMARY. 1. Resonance is a long, low-pitched, non-musical note, heard on percussing normal lung, due to unrhythmic, more or less localized vibrations. It may be imitated by percussing a loaf of fresh bread. It is associated with a sense of resiliency.

2. Tympany is a long musical note of variable pitch, produced by percussing elastic, air-containing viscera. It is due to widespread rhythmic vibrations and may be heard over the stomach, intestines, over relaxed lung tissue, and over many cases of pulmonary cavitation and pneumothorax. It may be imitated by percussing a loaf of stale bread or towel folded many times upon itself, or the inflated cheeks.

3. Dulness is a short, non-musical, invariably high-pitched sound, heard when percussing structures containing little or no air. It is due