their existence supposes a low state of vitality, such as, if inflammation is once introduced, will afford no very effectual resistance, but will allow the pneumonitis to assume the asthenic form.

Besides, if the inflammation seizes upon the comparatively well lung when the other is tuberculated, or seizes on the comparatively well portion of the lung, the other portion being tuberculated, the patient is, of course, embarrassed in his power of respiration and arterialization of the blood, and is liable to sink in death, as the immediate consequence. If, however, the effect is not directly fatal, still the increased prostration given to the system by the pneumonitis, detracts from its power to carry on the functions of life, and, of course, has the effect to hurry on the progress of the tuberculous disease. Indeed, post mortem examinations have shown that the lungs of persons dying of pneumonitis, complicated with phthisis, exhibit the gray tubercles thickly disseminated through the parenchyma. This fact alone is sufficient evidence that the secondary disease has given a new impulse to the primary.

No illustrations of the symptoms of secondary pneumonitis are necessary; nor any special rules of treatment. What I have heretofore said will suggest all that is important.

CHAPTER VI.

PULMONARY EMPHYSEMA.

Emphysema, in Greek supusnua, from the verb supusaw, to inflate, literally signifies an inflation; but applied a little less indefinitely, it signifies a soft tumor arising from air admitted into areolar tissue. In this sense surgeons still use it, to express that puffiness which arises from the admission of air into the areolar tissue, in connection with the occurrence of a compound fracture. In this case, however, the most common source from which the air is received, is the lungs. Suppose, for instance, a rib is fractured, and a bone has broken through the pleura and wounded. the lung. The air, passing directly into the areolar tissue, diffuses itself over the chest, neck, and other parts. It may even pass

some what extensively over the body. The parts thus affected give a peculiar sense of crackling, when pressed by the fingers.

The disease, however, of which I am now to speak is pulmonary emphysema, or air in the parenchyma of the lungs. For brevity's sake, this is commonly spoken of simply as emphysema, -the epithet descriptive of locality being omitted. But emphysema, in this sense, is divided into two kinds, vesicular emphysema and interlobular emphysema. In the former kind, the air is pent up in the vesicles, dilated to a greater or less extent. In the latter, it is effused into the areolar tissue, or held in its meshes, between the lobules, and beneath the pleura.

SECTION I.

VESICULAR EMPHYSEMA.

PATHOLOGY.-The enlargement of the cells, in this case, is very analogous to that dilatation of the bronchial tubes already described. In fact, a slight modification of the causes which produce the one will evidently produce the other. In the normal state, the vesicles are of such a size as barely to be discoverable by the eye; but, when enlarged by emphysema, they very commonly attain to the size of a millet-seed, and may become much larger. Sometimes sacs of the size of a pigeon's or even a hen's egg form; but, in such cases, most unquestionably several vesicles rupture in such a manner as to form one cavity. In other words, they break into one.

The sacs thus formed, by crowding against one another and against the more healthy pulmonary tissue, are made to assume various shapes, according to the accidental pressure. If the surface of a lung affected with vesicular emphysema be examined, the dilated vesicles can be seen through the pleura. Where they are equally enlarged, they appear like healthy vesicles viewed through a magnifying glass. But, sometimes the vesicles of one lobule are enlarged, while those of an adjoining one are of the natural size. In such a case, the emphysematous lobule becomes conspicuous by its protrusion; and the intermingling of those in an abnormal and those in a healthy condition, render the

surface quite irregular and uneven. Sometimes a large globular prominence is seen resembling a small bladder; but this, when examined, will be seen to arise from a depression into the lung of essentially the same size as the elevation without. Of course, a bulla of this kind cannot be passed about, as can the sub-pleural collections of air in interlobular emphysema.

Under the pressure of the finger, an emphysematous portion of lung crackles, like a piece of healthy lung, when dried. The walls of the vesicles, having lost their elasticity, have become rigid. The emphysematous portions, also, are pale,—sometimes almost white. Occasionally, the parietes of the lung appear as if they had been bleached. This paleness is most seen towards the free edges of the lung. "Sometimes these edges are rounded and thick; sometimes thinner and folded back; while, sometimes, the margin is blown out, as it were, into an irregular fringe; some of the inflated portions remaining connected with the lung by slender pedicles, and these forming appendices to it, of a light yellow color," appearing like a fringe of fat. If this emphysematous border be held between the eye and the light, it will appear translucent. If it be punctured, the surrounding parts collapse, proving that the dilated vesicles communicate with each other.

The size of an emphysematous portion of lung is increased, and the tissue becomes specifically lighter, so as to float light on water, like a bladder filled with air. The increased size causes a pressure against the ribs and the intercostal spaces, and distends the walls of the chest at the part corresponding with the distended portion of the lung. There is, consequently, at this part, a protuberance, which sometimes becomes very marked. Sometimes, however, so large a portion of the lung is affected, that one side of the thorax seems generally distended.

The emphysematous portion of the lung, which is generally the anterior margin, becomes comparatively anæmic, while the posterior portion is not so affected, but sometimes even becomes congested in consequence of the attending dyspnoea. In vesicular emphysema, the morbid condition, once introduced, generally continues and gradually becomes worse. The interference with the nutrition of the lung renders it less able to resist the cause of

the affection; and, hence, the disease is almost necessarily progressive.

tence.

Vesicular emphysema is very liable to be complicated with other diseases. In the first place, it is probable that bronchitis, either acute or chronic, is usually the leading cause of its exisThe inflammation of the acute form, or the thickening of the membrane in the chronic, it is easy to conceive, may so affect the entrances into the vesicles that, while the air is readily forced in, in inspiration, it does not as readily return in expiration; and, hence, the liability of the vesicles to become permanently enlarged. The air being incarcerated and accumulating in the vesicles, they yield to its distending force and lose their elasticity. If, at the same time, there exists a hard cough, the forcible efforts. made will increase the difficulty.

But, besides this connection of vesicular emphysema with bronchitis, the former disease is liable to induce the latter, and thus stand to it, in the relation of cause, as well as effect. The embarrassment of the respiration and the agitation produced necessarily determine more blood to the neighboring tubes, producing congestion and the liability to inflammation or bronchitis. The congested or posterior portions of the pulmonary tissue, too, readily pass into a state of inflammation, constituting pneumonitis. Again, the obstruction of the blood in passing through the lungs prevents the right side of the heart from emptying itself freely. The consequence is palpitation, or increased muscular contractions of the right ventricle, followed by a "yielding of its walls to the augmenting pressure of the contained blood." Of course, this embarrassment in the circulation is greatest when the dyspnoea is greatest; but the right cavities of the heart become permanently dilated, and the dilatation leads to anasarca, particularly edema of the feet and ankles. Finally, the opinion has prevailed, that asthma is induced by this disease; and it is easy to see how the nervous system may become so affected by it as to constrict the bronchial tubes. The manifestations of emphysema, however, so far resemble those of asthma, that the one disease has evidently been often mistaken for the other.

Having referred to one-perhaps the principal-cause of emphysema, I now add farther, that, besides bronchitis, any thing

else which impedes the free exit of air from the lungs may produce it; and, among the other causes, may be reckoned blowing on wind instruments, and pressure made on parts of the lung, as by a tumor in the thorax, an enlarged heart, an aneurism, tight lacing, or a deformed condition of the chest.

DIAGNOSIS.-Among the general signs of vesicular emphysema, an habitual shortness of breath, with occasional paroxysms of extreme dyspnea, is prominent. In a case of moderate severity, the patient is conscious of a little shortness of breath, on walking up a hill or making some unusual exertion. In an extreme case, the act of ascending a few steps of a staircase will render him breathless. The paroxysms of dyspnoea will frequently occur without any assignable cause, and, when existing, will oblige the patient to sit erect or lean forwards. In such a case, the

muscles of respiration are thrown into violent action; the face becomes livid and swollen, and great constriction is experienced at the præcordia.

There is, also, in this disease, a cough which is somewhat peculiar. At first, it is rather dry and wheezing; or there is, to a small extent, an expectoration of thick pearly sputa, but, after paroxysms of dyspnea are established, there is a more copious ejection of a thin, glairy, and transparent matter. Palpitation of the heart, and that secondary consequence, oedema of the ankles, are also among the general signs of this disease.

The physical signs in a well developed case of vesicular emphysema are distinctly marked. They are principally these,— the distention of a portion of the thorax, diminished movements of its walls, resonance on percussion, a peculiar feebleness of the healthy sounds of respiration, and the emphysematous crackling. The last, when heard, is pathognomonic of the one or the other form of emphysema.

The distention of the thorax is necessarily the greatest in those portions in which the dilatation of the vesicles is the greatest, and those, I have already said, are at the anterior margin of the lungs. Hence the anterior thoracic plane becomes decidedly convex. The form of the distended portion is generally rather oval, having its long diameter parallel with the axis of the body. It is,