FIG. 67.

FIG. 68.

FIGS. 67 AND 68.-The solid lines indicate the position of the pulmonary margins and of the interlobar fissures. The dotted lines mark the anterior and lower confines of the pleural cavities-the spaces into which the lung expands during forced inspiration. This space at its lower margin, which is bounded by the diaphragm on the inside and the thoracic wall on the outside, is known as the complemental space of Gerhardt. It is in this space that small pleural effusions first accumulate, thus causing the disappearance of the diaphragmatic shadow (see p. 28), slight dulness on percussion and diminished vocal fremitus, resonance and breath sounds.

level of the fifth thoracic vertebra, indicates the level at which the trachea bifurcates, and anteriorly the upper point at which the lungs meet, to diverge again at the fourth costal cartilage. It marks the upper boundary of the cardiac auricles, and the point at which the veins of the hand collapse while the arm is being raised upward from its lowest to its highest position (Gaertner's test of venous blood pressure). It forms a convenient landmark from which to count ribs.

FIG. 69. An approximate knowledge of the location of the pulmonary fissures is especially important in the diagnosis of interlobar empyema. Right lung. The fissure between the upper and the lower lobe corresponds to a line drawn from the fourth dorsal vertebra to the fifth or sixth costo-sternal articulation. The upper border of the middle lobe is marked by a line drawn from the middle of that just described, to the third costo-sternal articulation. (After Doyen, Bouchon and Doyen.)

FIG. 70.-Left lung. The interlobar fissure may be located by drawing a line from the fourth dorsal vertebra to the sixth costo-sternal articulation. These relations are not absolutely fixed, but are subject to individual variations. (After Doyen, Bouchon and Doyen.)

The vertebral spines correspond to the level of the rib below. The first rib begins and is in direct articulation with, the seventh cervical vertebra. The second rib articulates with the second and third vertebræ, the third rib with the third and fourth vertebræ, etc., but the eleventh and twelfth ribs articulate directly with their respective vertebræ. The scapula overlie the second to the seventh or the third to the eighth ribs. The hilus of the lung lies opposite to the spines of the fourth, fifth and sixth, and the bodies of the fifth, sixth and seventh, vertebræ.

FIG. 71.-Vertical section of the body, showing the shape of the lower lobes, the upper lobes having been removed. Note the higher position of the right phrenic dome, which causes the lower border of pulmonary resonance to be slightly higher on the right side. On the left the stomach imparts a tympanitic quality to the lower portion of the lung. If filled with food it diminishes pulmonary resonance and may simulate consolidation or a small pleural effusion.

CHAPTER VI

METHODS AND RESULTS OF PERCUSSION

The Immediate or Direct Method. The hand or the finger tips are struck directly against the object in which we desire to set up vibrations. This was the method of Auenbrugger, who, however, covered the fingers with a soft glove to diminish the finger element of the sound, especially the overtones. The direct method is still occasionally employed to determine the resonance of the upper lobes of the lung (by using the clavicle as the pleximeter), or that of the lower lobes as a whole, by striking the patient's back with the edge of the hand.

The Mediate or Indirect Method. This was suggested by Piorry, who interposed a hard object-the pleximeter-between the plexor (the object striking the blow) and the part to be percussed.

Artificial plexors and pleximeters are sometimes used, especially for class demonstration. They generally consist respectively of a small light rubber-tipped hammer, and of a narrow piece of bone or vulcanite of variable shape (Fig. 72). The fingers are nearly always used as plexor and pleximeter.

The middle finger of the left hand is pressed firmly against the chest wall, in a direction parallel to the ribs, while the middle finger of the right hand strikes upon it, just behind the nail, a short, light, quick, vertical blow, delivered from the wrist (Figs. 73 and 74).

The Pleximeter. Despite the fact that a hard pleximeter, a quick rebound and a short time of impact are advantageous, we cannot use an unpadded plexor of hard material because in such a case a high-pitched sound would be produced, due to the overtones of the pleximeter which would overshadow the low-pitched fundamental note of the lung. We therefore use a soft plexor or the finger, just as we use felt pads in a piano in order to let the basic note preponderate and to drown out the unharmonious overtones. The vibrating area equals in size the percussed area plus a radiation during the course of transit. Hence the smaller the pleximeter and the more superficial the tissue percussed, the more accurate our topographic results (see Fig. 75).

Half the diameter of the pleximeter must always be allowed as the unavoidable margin of error in estimating the boundaries between an air-containing and an airless structure as the heart and lung, even when the pleximeter is applied in a direction parallel to the anticipated boundary line. Based upon these facts some very narrow, wedge-shaped pleximeters (Ziemmsen) have been devised for limiting the lung apices, cardiac boundaries, etc. The results derived from their employment, however, have been disappointing (Fig. 72),

The percussion blow may be delivered either lightly or forcibly, and accordingly we speak of light or heavy-superficial or deep-percussion. The latter terms are used because with heavy percussion a deeper penetration of the vibrations is ensured-the sphere of the blow is largergreater masses of tissue are set in vibration and a louder sound is produced.

FIG. 72.-1, Plexor or percussion hammer; 2, ivory pleximeter; 3 and 4, Hirschfelder's pleximeter; 5, Sansom's pleximeter.

FIGS. 73 AND 74.-The method of percussion. The percussion blow is struck from the wrist only, the forearm being practically stationary. The impact, which is delivered just behind the nail of the middle finger, should be quick and brief in duration, the force of the blow should fall as vertically as possible. Fig. 73 shows the beginning, Fig. 74 the end of the percussion stroke. In order to deliver a vertical blow with the terminal phalanx, the nail of the second finger, which is generally used as plexor, must be short.