There are forms of bronchial dilatation besides that which depends on the wasting of the tissues in old age, or senile marasmus. In fact, this portion of the air-passages is remarkable for the frequency with which dilatations occur, and for the degree of development which they attain. They constitute one of the most important diseases of the air-passages.

1 See Oesterr. Jahrb. vol. xvi. p. 3.

There are two forms of bronchial dilatation which especially claim our attention: a. In the first we find a bronchial tube uniformly dilated through a certain extent; that is to say, the dilatation has taken place uniformly at all points of its periphery, so that a tube, which in the normal state will admit only of a fine probe, will now admit of the passage of a crow or goose-quill, or even of a larger body. The dilatation is very striking and distinct, when we see a bronchial tube far exceeding in size the stem from which it is given off. It is seldom confined to a single tube, but, as a rule, affects a distinct portion of the bronchial tree; and its branches and twigs may either undergo an augmentation proportional to their relative natural sizes, or, as is more frequently the case, the dilatation becomes more considerable the deeper and further we proceed. In this it observes a law to which we shall frequently recur.

B. The second form is the saccular dilatation. Here we find a bronchial tube dilated into a fusiform or roundish sac; the dilatation in the latter case very frequently preponderating in such a direction, that the greater space of the bronchial sac lies altogether out of the axis of the tube entering or leaving it. These sacs, in rare cases, attain the size of a hen's egg, but most commonly they are of the size of a bean, hazelnut, or walnut. We find, also, that either one or several bronchial tubes may undergo this saccular dilatation, while on both sides of the sac the normal calibre is retained, or the whole bronchial ramification may be affected. In the latter case, numerous similar sacs of various sizes are so arranged, that, collectively, they form a large ramifying sinuous cavity, whose individual excavations are bounded and separated from one another by ridge-like or valvular duplicatures, projecting inwards from the bronchial walls. Saccular dilatation of the bronchial extremities constitutes a special variety, which is frequently observed in the form of thin membranous vesicles, completely filled with air, and occurring, either singly or in groups, in the vicinity of cicatrizing tubercle in the apices of the upper lobes. One or more bronchial tubes, in taking their course through the impermeable substance of the apices of the upper lobes, crowded with obsolete and cretified tubercles, and, as it were, saturated with pigment, become compressed by the shrivelled parenchyma, and are finally obliterated; their extremities then expand into the above-mentioned vesicles; and, according to the state of the bronchial tubes - whether they are merely compressed or actually obliterated - the sacs may be emptied by gradual pressure, or will resist all attempts to expel the air.

Of these two forms of bronchial dilatation, the second appears to be the more common, and in young persons is undoubtedly the more frequent. The degree of dilatation may be determined by the proportion which it bears to the size of the bronchial tube, and to the calibre of the parent stem, from which it is given off. From the observations we have already made, it is obvious that, while its extent may be very limited, it may on the other hand be so considerable, that all the bronchial tubes of one lobe, or even of a whole lung, may be thus affected.

Bronchial Dilatation

Bronchial Dilatation occurs, for the most part, in the smaller tubes, and, as a general rule, is most frequent and, at the same time, most extensive, in those of the third and fourth order. It is never found in the two primary bronchi, or, at all events, very rarely, and then in the same form as the tracheal dilatations already described.

The bronchi near the surface and borders of the lungs are most liable to this affection; and this fact may be regarded as one of the evidences (and there are others) of the affinity between this affection and true vesicular emphysema of the lungs. The upper lobes are the most common seat of bronchial dilatations.

The walls of the dilated bronchi are found in various conditions. Sometimes we observe the mucous membrane and the fibrous sheath hypertrophied and thickened. The former appears in a state of chronic catarrh, being tumid, of a more or less dark-red tint, of a loose spongy appearance, and permitting of being easily torn. The bronchi are rigid; on making a section of the lung, they appear like wide, gaping tubes from which a thick, yellow, purulent mucus is seen to flow, and their white, thick fibrous sheaths strongly contrast with the inner layer of tumid and reddened mucous membrane. Such is the usual character of the first form of bronchial dilatation.

In the saccular form of dilatation, the walls are relaxed and attenuated. The mucous membrane of the bronchial sacs is only slightly, or not at all, reddened; it is more commonly pale; the firmness of its tissue is very little, or not at all, modified; and it generally presents a smooth and polished appearance, similar to that of a serous membrane. The sacs contain a thin, pale-yellow, puriform fluid, or an almost colorless vitreous mucus.

From the very striking and almost constant differences presented by the bronchial walls in these two forms of dilatation, we are led to infer that there are corresponding differences in their nature and their causes; and we shall presently have an opportunity of pointing out in what these differences actually consist.

The pulmonary tissue surrounding a bronchial dilatation is generally of increased density, and finally becomes obliterated. We shall subsequently enter fully into the consideration of this change, and the conditions giving rise to it; and shall point out its importance in the establishment of a theory relating to the production of bronchial dilatation.