so-called susceptible individuals will be affected, while those with healthy tissues with normal or a high resistance will be able to destroy or to localize the invading host.

(352) Pathology of Tuberculosis.

Some of the naked eye appearances of tubercle and tuberculous ulceration are represented in plates II, III, IV—

Plate II (c) represents the spleen of a guinea-pig affected with general tuberculosis from the injection of a culture into the anterior chamber of the eye (after Koch).

Plate III (c) represents the lungs of a guinea-pig infected by inhaling dried tuberculous sputum (after Koch).

Plate IV (b) is a portion of the small intestine from a Cariama (Cariama cristata), the blood-vessels of which have been minutely injected. It exhibits very small masses of tuberculous matter raised a little above the surface of the mucous membrane. The paleness of the tuberculous matter contrasts strongly with the bright redness of the mucous membrane (Royal College of Surgeons Museum. No. in Catalogue 2,546). (c) represents a tuberculous ulcer in the human ileum. The surfaces are but little indurated though very vascular, and the floor of the ulcer presents a yellow caseous appearance. There are also several small tubercles (Royal College of Surgeons Museum. No. in Catalogue 2,547).

Both these ulcers may be compared with (a), which represents a portion of the human ileum affected with a typhoid ulceration of one of Peyer's patches (Royal College of Surgeons Museum. No. in Catalogue 2,499).

The pathology may be studied conveniently under two divisions, viz., that of pulmonary tuberculosis and that of miliary tuberculosis. The most recent contribution to and summary of the pathology of the disease is the research of Dr. Sims Woodhead, and the following account is an abstract of Dr. Woodhead's paper on the subject.

(353) The Pathology of Pulmonary Tuberculosis.

It is now generally accepted that all cases of rapid infective phthisis are the result of the action of the tubercle bacillus,

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although it cannot be denied that certain lesions may be produced as the result of the action of other non-specific irritants. In these conditions, however, tubercle is very frequently associated with some other lesions, and it is often extremely difficult to say what changes are due to the one and which to the other. For instance, it has long been held that in stonemasons' phthisis all the characteristic lesions met with in chronic tubercular phthisis are present, but Dr. Woodhead's experience of stonemasons' lung has been that along with the chronic interstitial and arterial changes, set up by the stone particles, there are structural alterations which can be accounted for only on the assumption that they are of tubercular origin, and in some few cases, in confirmation of this, the presence of tubercle bacilli has been demonstrated in certain of the new growths. In the first instance we should expect under given conditions the mucous surface of the bronchus to be attacked. Such an assumption might most fairly be made after a consideration of Julius Arnold's observations on the course taken by dust when inhaled into the respiratory passages, Arnold pointing out the important part played by the walls of the small bronchi and their terminal passages in the disposal of inhaled dust particles. Secondly, there is the alveolar epithelium, which under the influence of any irritant material undergoes proliferation more or less rapid, this in certain. cases terminating in what we know as catarrhal pneumonia. Here, again, in proof of the statement, take what may be seen under the microscope, when particles of coloured dust have been inhaled into the lung. The cells lining the alveoli are seen to be in an active state of division; some are still adherent to the walls of the air vesicle, and in these small particles of the pigment may be seen embedded in the protoplasm. The epithelium in this position is a structure which may be attacked by tubercle bacilli, just as in it coal or other particles may be found. Passing still further, and following the course taken by the pigment granules, the lymph spaces around the air vesicles are reached, then the lymphatics in the interstitial and interlobular tissue, the peribronchial and perivascular lymphatics, and lastly the glands at the root of the lung, either directly or by deep layer of the pleura, over the surface of the lung, and so to the root. As may be seen on reference to a section of coalminer's lung, the pigment (in this

instance a material which gives rise to little irritation) is carried to every part of the lymphatic system, and is seen to have accumulated in very considerable quantities along the lines of the septa, around the bronchi and blood vessels, and in the deep layer of the pleura. On microscopic examination, the pigment acting as an irritant, and so giving rise to a slight excess of fibrous tissue in all these various positions, may also be seen. Lastly, the small points of lympathic tissue which occur at intervals along the lymph channels, first described by Burdon Sanderson, then by Klein, Arnold, and others, are the seats of pigmentation. Tubercle formation may also be met with in any of these positions. It would seem at first sight to be an easy matter to determine at once in what tissue the tubercle has originated in any special case. In the lung, however, where the tissues are so delicate and so complicated, and where in consequence the changes are so rapid, this is not the case; and it is only in exceptionally favourable cases that the mode of origin and spread can be at all satisfactorily demonstrated. Further, the variety in the life histories of individual tubercular growths at one time rendered it a matter of considerable difficulty. to arrive at any definite understanding of tuberculous processes, especially of those associated with pulmonary phthisis. The anatomical structure in the various forms being so absolutely defined in the earlier stages of the growth, it was difficult to bring into a common group forms which differed so widely from one another, not only in naked eye but in microscopic appearances.

There is now, however, sufficient evidence to justify pathologists in stating that many of those forms which different clinical observers have from time to time described as tuberculous are undoubtedly tubercular in character, from the small grey, gelatinous, or fibroid nodule, to the large caseous masses, leading to cavity formation; and the presence of the specific bacillus has time after time been demonstrated in all these forms, both by staining and by inoculation. There can be little doubt that these forms are essentially the same, and that the differences observed are due first to the resisting power of the tissue attacked, and secondly, to the numbers and activity of the attacking bacilli. If the behaviour of other tissues under the action of mechanical or micro-organismal irritants be borne in mind, there will be little cause for wonder

that there should be these numerous varieties of manifestation of the action of the specific irritant in tuberculous lungs. In connection with this statement, a matter may be insisted upon to which, as a rule, far too little importance is assigned-viz., the intercurrence of suppurative changes, which are evidently set up by the activity of a different micro-organism.

Both Dr. Woodhead and Mr. Hare were much struck by the fact "that after one micro-organism has completed its task another may step in and continue the process of breaking down. How frequently a pyæmic condition supervenes on a tubercular. How often has a patient suffering from tubercular abscess of the kidney or of the lungs succumbed at last (if not carried off by acute tubercular disease) to pyæmia, and pyæmia in which the symptoms are extremely well defined." How frequently localized suppuration steps in to aid in the breaking-down process, more frequently in the lungs and in the intestines than in other positions, because of the greater ease with which organisms giving rise to the irritant material can arrive at and remain on the tubercular surfaces in these organs. Writing on this subject, Coats, in his Lectures to Post-graduates, points out that tubercle is essentially a disease of surfaces and channels, and this is so far true that bacilli can reach the tissues only by such surfaces and channels, and that in these channels there are irritant secretions often containing numerous micro-organisms and other products which assist in completing and hastening the breaking-down process commenced and partially continued by the tubercle bacilli. The actions and interactions in these cases are extremely complicated, and but for the occurrence of more simple cases now and again the observer would be completely lost amongst it all. Of 100 cases, in which there was tubercle of the mesenteric glands, the mediastinal glands, or the glands at the root of the lung, were also distinctly affected in 69 cases, whilst in 62 cases the lungs themselves were affected. Of these 62, 59 were included under the 69 in which the glands at the root were tubercular, the other three having developed first simple catarrhal pneumonia, which had later become tubercular in character (in two of these bacilli were found). There were also, as the figures show, seven cases in which, although the glands at the root were affected, there was no tuberculous process in the lungs

1 Pathological Mycology, p. 13.