immediately beneath the part percussed. If these precautions are carefully attended to, the physician will generally be enabled, especially in thin persons, to arrive approximately at a correct conclusion. The following are the sounds ordinarily emitted by the chest on percussion when the patient is in a state of health.

In the præcordial region, where the heart, uncovered by lung, comes into immediate contact with the chest walls, percussion yields a short, dull sound, and conveys a sense of strong resistance to the finger. The spot where this is most distinctly marked is between the fifth and sixth ribs on the left side. When percussion is practised towards the boundaries of this uncovered space, the sound becomes somewhat clearer and more resonant, and the resistance less, in consequence of the proximity of the lungs; and in those parts where the lungs overlap the heart, and lie between it and the chest walls, the resonance and the sense of resistance to the finger vary according to the thickness of the intervening stratum of lung tissue and to the force of the percussion stroke.

The gentler the percussion employed—a gentler tap with one finger answers best the more clearly the pulmonary resonance is brought out. The greater the thickness of the stratum of lung, the clearer and more pulmonic will be the resonance. The area over which more or less of dulness may be elicited by forcible percussion corresponds to that occupied by the heart and great vessels, and this has been already pointed out.* Suffice it to say, that it extends vertically from the upper border of the third to the lower margin of the sixth left cartilage, and transversely from about half an inch to the right of the left nipple to about half an inch beyond the right margin of the the sternum, opposite the fourth sterno-costal articulation. Of course the act of respiration, change of posture, and other circumstances which have been already referred to as influencing the position of the heart affect the area which is left uncovered by the lung, and exert a corresponding modifying effect on the result of percussion. Inspiration especially, by inflating the pulmonary tissue, forces the left lung in front of the heart, and diminishes the area of dulness, whilst expiration usually increases it.

In disease the area of præcordial dulness is liable to greater variations than it is even in health, and its increase or diminution, as the case may be, may exist in the heart itself, in its pericardium, or in disease external

* See chapter on the topography of the heart and great vessels, pp. 1, 2.

to, and independent of it. Ranged in a tabular form, the causes of increased præcordial dulness may be stated as follows:

First. External to the heart and pericardium.—a. Morbid growths or abscess in the anterior mediastinum, or in other parts of the chest, encroaching on the mediastinum. b. Aneurism of the aorta or other great vessels. c. Consolidation of the pulmonary tissue. d. Pleuritic effusion in the left pleura, encroaching on this region. e. Retraction of the left lung, consequent on pleural adhesions, whereby a greater surface of the heart is brought into contact with the chest walls. f. Enlargement and upward pressure of the liver, especially of its left lobe.

Secondly. Existing in the pericardium.-a. Effusions, whether of serum, lymph, pus, or blood into the pericardium. b. Tubercular or cancerous deposits, which are usually attended by serous or serosanguineous effusion.

Thirdly. Existing in the heart itself.-a. Hypertrophy of the heart, b. Dilatation of the heart; c. Dilatation of the heart, attended by hypertrophy of its walls.

The causes which lead to diminution in the area of præcardial dulness are to be found in like manner in the heart itself, in the pericardium, or in disease external to it. Ranged in a tabular form, they may be as follow:

First. External to the heart and pericardium.-Pneumothorax and emphysema of the lung.

Secondly. Existing in the pericardium.-Effusion of air into the pericardium.

Thirdly. Existing in the heart.—Atrophy of the heart.

The causes external to the heart and pericardium which operate in producing extension of the præcardial dulness scarcely call for any remarks. Their action is self-evident, and so also is the fact that they may and possibly would occasion considerable difficulty in the diagnosis. Indeed, it often happens that the true nature of the mischief cannot be arrived at merely by the aid of percussion, and that it would escape detection if the other physical signs and the general symptoms were not appealed to. Perhaps the only lesion which requires special notice is aneurism of the aorta, or other great vessels. It must always be remembered that the extent of surface over which the presence of an aneurismal sac gives rise to dulness on percussion affords no clue to the size of the aneurism, inasmuch as from its globular form, the tumour may not come extensively in contact with the chest walls. Further, aneurism of the

aorta, even of considerable size, if arising from the posterior portion of vessels deeply seated in the chest, cannot be detected by percussion without much difficulty, especially if the patient be stout, whereas, in a thin person, a small aneurism, no larger than a walnut, if arising from the upper and anterior surface of the aorta, towards the right angle of the arch, will generally give rise to sufficient dulness on percussion to ensure its detection on careful examination.

The causes of increased præcordial dulness existing within the pericardium demand a more lengthened comment. Fluid of whatever kind in the pericardial sac, whether consisting of simple serum, the result of passive effusion or of active dropsy, or of serum mixed with lymph or pus, or blood, the products of pericardial inflammation, or of blood resulting from an injury to the heart, or from the oozing of an aneurism, must necessarily produce extension of the limits of normal dulness on percussion; and under favourable circumstances, four or five ounces will suffice to do so. In such a case the increase of dulness will be chiefly perceptible towards the base of the heart; for the pericardium admits of distension upwards more readily than in any other direction ; and in a recumbent posture the heart, if unrestrained by adhesions, would also have a tendency to rise upwards.

On the other hand, when fluid has accumulated to a large extent, the elasticity of the pericardium is impaired, and the sac may undergo enormous distension-not upwards only, but backwards, laterally, and even downwards. It still retains its pyramidal form, its broad base resting on the diaphragm, and its apex seated behind the upper part of the sternum; but in cases of extreme distension, the apex may protrude even above the clavicle,* and the base pushing the diaphragm downwards, may cause a slight fulness in the epigastrium, whilst laterally its walls may extend almost from nipple to nipple, and may produce condensation of the inner and anterior margins of the lungs. In such a case as this the percussion sound is absolutely dull over the entire surface covered by the distended pericardium, and the resistance to the finger is very great, just as in pleuritic effusion.

More commonly the amount of fluid is smaller, and the pericardium, though distended, does not reach above the level of the second sternocostal articulation; but it pushes aside the anterior borders of the lungs,

* This occurs only in cases in which the patient retains a recumbent posture. More commonly the patient sits erect or leans forward, resting the elbows on the knees, and then the dulness rarely extends above the second sterno-costal articulation.

and comes into immediate contact with the chest walls. The result is the production of dulness on percussion, traceable over an area which in ordinary cases extends from the second costal cartilage above to the cartilage of the sixth rib below, and laterally from the left nipple to about an inch, or even more, to the right of the sternum.

Percussion affords material aid in distinguishing between pericardial effusion and hypertrophy with dilatation of the heart. The dulness of pericardial effusion is developed more rapidly than that due to hypertrophy of the heart; it reaches higher in the chest, and extends lower down; it shifts its position more completely under change of posture; it is more intense in character, and yet it is only of temporary duration, and the resistance to the finger is greater. Of course, if the exudation consist principally of plastic materials, the seat of dulness will not be so readily altered by change of posture as if the effusion consisted principally of serum, nor will the dulness rise so high in the chest, nor will it disappear so speedily; but it will be developed much more rapidly than hypertrophy of the heart, and may be readily distinguished from it by other means of diagnosis.

The effect of tuberculous or cancerous deposits in the pericardium necessarily varies with their extent and position. If they are extensive, and seated on the lateral margin of the anterior surface of the heart, they necessarily give rise to an increase in the area of dulness, even though they be not accompanied by effusion into the pericardium; whilst if seated behind the heart, they are apt to push that organ forward, and thus, by causing displacement of the anterior margins of the lungs, lead to an extension of the præcordial dulness. When accompanied, as they often are, by effusion into the pericardium, the fluid gives rise to still further extension of the area of dulness.

The causes of increased præcordial dulness existing in the heart itself are also deserving of attentive study. They are hypertrophy, hypertrophy with dilatation, and dilatation without hypertrophy. In either form of disease both sides of the heart may be hypertrophied or dilated, or the enlargement may be confined to the right or to the left side. The augmentation of bulk may vary from a slight amount, which it is difficult if not impossible to detect by percussion, up to the enormous size of a heart, mentioned by Dr. Williams, which weighed forty ounces, its * Dulness referable to an hypertrophied heart does not, until the disease is far advanced, extend above the third left rib or below the sixth.

circumference round the base being fourteen and a half inches, its length, from the arterial orifices along the septum to the base, eight and a half inches, and the thickness of the left ventricle one to four inches; whilst near the columnæ carneæ it measured from one to five inches. In the case of even a much smaller increase of bulk than is here recorded, the lungs are pushed aside, and an unusually large surface of the heart comes into immediate contact with the chest walls, and leads to an extension of the area of præcordial dulness on percussion, and to a sense of increased resistance.

When the hypertrophy is general, and especially when it is combined with dilatation, the heart sinks downwards, in consequence of its increased weight, and its change of position is often to the full extent of the increase in its vertical diameter. From the horizontal position in which it necessarily lies, its apex beats far to the left of its usual seat of impulse, often, indeed, to the left of the nipple. It follows, therefore, that in most instances of cardiac hypertrophy an increase in the area of the percussion dulness will be perceptible in that direction. But it should be clearly understood that when the patient has been lying flat in bed for a considerable time the heart is apt to fall backwards, and even upwards, to such an extent that no downward extension of the percussion dulness may be perceptible, but, on the contrary, some extension of the dulness upwards-and this the more so when the left auricle is much dilated and hypertrophied. In several such cases I have known extension of the dulness at the base extremely well marked.

When the hypertrophy or dilatation occurs principally on the left side of the heart, the extension of dulness on percussion will be to the left, or to the right if the right cavities are the seat of enlargement.

It is only right to add, however, that when hypertrophy or dilatation exist in only a slight degree, there is nothing more difficult than to determine the fact by percussion alone. Even when the disease is further advanced, its diagnosis, by the aid of percussion, is often extremely uncertain, inasmuch as it is frequently accompanied by emphysema of the anterior margin of the lungs, and if a portion of emphysematous lung forces itself between the heart and the chest walls, the dulness which would otherwise be produced by the enlarged heart is masked, and the outline of the organ cannot be satisfactorily ascertained.

Dr. Walshe and some other authorities have stated that old adhe