separating them also disintegrates, and then the one opens into the other and a larger vomica results.

It sometimes happens, however, that a considerable portion of a catarrhal lung caseates very rapidly, and breaks down almost like a slough. In such a case the obliterated condition of the bloodvessels leading to the part, such as that shown in Fig. 25, is apparently the cause. As has been demonstrated by Friedländer and others, an obliterative affection of the branches of the pulmonary artery, such as that seen in syphilis, is of common

a

b

FIG. 24. Catarrhal pneumonia, third stage, × 50 diams.

a, the cavity formed by dissolution of the centre of the caseous pneumonic mass; b, the caseous edge; c, the compressed air-vesicles filled with caseating catarrhal products.

occurrence in phthisical lungs. The figure above alluded to illus trates this. It represents a portion of a lung taken from the neighbourhood of a phthisical cavity, and, in its centre, is shown a transverse section of a small branch of the pulmonary artery leading up towards the cavity. The lumen, or, rather, all that remains of it, is shown at b, its small size in all probability, having completely prevented the passage of blood. The diminution in size is caused by the thickening of the tunica intima (a), whose inordinately great dimensions are apparent.

Around the obliterated artery are several air-vesicles containing caseous catarrhal products, all in a more or less disintegrated condition. Now, when this obliterated state of the arterial branches supplied to an already infiltrated portion of lung becomes general over a wide area, it can easily be perceived how the diminished arterial supply will deleteriously act upon it, and tend to cause necrosis and disintegration en masse. This undoubtedly accounts for the presence of those large, rapidly formed cavities seen in certain phthisical lungs.

a

FIG. 25. Catarrhal pneumonia, third stage, × 50 diams. Shows the obliteration which occurs in the branches of the pulmonary artery. a, thickened tunica intima of a branch of the pulmonary artery leading up to a cavity; b, the narrow lumen of the same; c, air-vesicles filled with caseous catarrhal secretion, and beginning to disintegrate.

Small aneurismal dilatations of some of the vessels are occasionally found in phthisical cavities. They are usually about the size of a horse-bean, and by their rupture cause sudden death from profuse hæmoptysis.

The question of how far it is possible for a large phthisical cavity to cicatrize is, of course, one of the greatest importance. Were it not that the lung is in reality fixed to the costal wall, by the adhesions which occur in the second and third stages of the disease, it might be possible for shrinking to occur to an extent sufficient to obliterate a cavity even of considerable size. Were the cavity situated in an organ such as the liver, for instance, it is conceivable, nay, likely, that closure of it would

ensue by cicatrization, if the débris were removed from its interior. The lung, however, is placed differently from the liver in regard to its surroundings. The costal wall being a fixed point, any cicatricial contraction in the lung-substance around such a cavity rather tends to widen than to diminish its interior. I hold it to be extremely questionable, whether a large phthisical cavity ever becomes obliterated by this means. I have never seen any post-mortem evidence of it. Small cavities probably do heal by contraction.

If closure is not likely to take place in a large cavity, another beneficial circumstance may and does, notwithstanding, frequently occur. The caseous material being all expectorated or absorbed from the cavity, its wall becomes fibrous from surrounding cicatrization, so as to render it no more dangerous a complication than a bronchiectatic cavity of equal dimensions. There is abundant evidence, both clinical and post-mortem, to show that patients may live with such a cavity, or cavities, in the lung for many years. The great danger to such subjects, is the further implication of the lung-tissue by the caseous pneumonic process, so that fresh areas of lung-parenchyma become infiltrated and destroyed.

The beneficial effects which phthisical patients experience from transference to an equable climate are, in all probability, due to there being little irritation caused by the inhaled air, and hence less liability to the excitement of catarrhal processes in sound portions of the organ. The lung has thus time afforded for cicatrization of those parts already implicated.

ON A PECULIAR FORM OF CATARRHAL PNEUMONIA WHICH IS LIABLE TO BE MISTAKEN FOR TUBERCLE.

It has previously been stated that little reliance should be placed on mere naked-eye characters in determining whether a nodular deposit in the lung is tubercular or not. I propose, before concluding this series of articles, to draw the reader's attention more particularly to this, as certain significant facts presently to be mentioned have an important bearing upon

the elucidation of the etiology of many instances of diffuse tuberculosis.

A child has indefinite signs of catarrhal pneumonia, passing, it may be, into those of general tuberculosis. The lung, after death, is found to be diffusely infiltrated with nodules, certainly sometimes a little larger than tubercles, but frequently as small or smaller. They have the same grey character at the periphery as tubercles, but are occasionally slightly yellow in the centre. Their shape is a little more irregular than tubercle, and in certain instances they tend to run together. Most of them, however, are quite isolated, and occur at intervals through the pulmonary tissue, very much as in primary tubercle of the organ. There is one point about this peculiar disease, however, which is significant. There is not any evident caseous source of infection in other parts, or in the lung itself. I have seen, certainly, tubercles in other organs in such cases, but these were evidently of later date, and corresponded to deposits secondary to those in the lung as an infecting centre. The history of such cases points to this being so, the meningeal or other tubercular disturbance being the climax of the disease.

The most curious point about these deposits is that they have not the slightest tubercular structure, but, in all respects, are identical with what is seen in the second stage of catarrhal pneumonia. They are small isolated groups of air-vesicles filled with epithelial products, the group invariably caseating in the centre. Every one has exactly the same appearance; there is not a vestige of any giant-cell structure; there is nothing of an interstitial character in the nodules. The whole process is one of catarrhal accumulation in the air-sacs, followed by necrosis of the mass; and the only difference between this and ordinary catarrhal pneumonia is, in the fact of the nodules being small in size, isolated in character, and universally disseminated throughout the lung-substance.

I am well aware that, in the early stages of primary tubercle of the lung, there is a very close resemblance in the tubercle nodule to a catarrhal pneumonic deposit. Still, in all these cases where there is a distinct caseous infecting source, I have never failed to detect, in some of the older nodules, distinct and undoubted evidence of the giant-cell structure. The tendency

to organization and isolation, which form two of the most characteristic features of the tubercular as contrasted with the catarrhal pneumonic lesion, is also invariably present. The above, however, never show any tendency of this kind, and their periphery never has the sharply circumscribed border, when seen microscopically, that the young tubercle-nodule has.

FIG. 26. Disseminated catarrhal pneumonia. A, the naked-eye appearance of a portion of lung affected with this disease. B, one of the nodules from A, magnified 50 diams. a a, air-vesicles filled with catarrhal cells; b, the caseous centre; c c, the air-vesicles filled and becoming obliterated by caseation.

In order to show the characters of the two deposits, I have prepared two sets of drawings illustrating each. Figure 26 A represents the naked-eye appearance of a small portion of a child's lung with the peculiar catarrhal pneumonic deposits in it, while Fig. 27 C gives the same view of a similar portion of a lung affected with primary tubercle, both of natural size. The close resemblance between them is apparent, so that, usually, with the naked eye, it is impossible to tell whether we have to do with a