But the presence of these tubercular nodules is irritating to the healthy lung tissue in the neighbourhood. This irritation causes an exces sive flow of blood to the neighbourhood, and an inflammation is produced with the characters of a pneumonia, the air-cells of the affected area becoming filled up with inflammatory material from the engorged vessels. Thus if these tuber cular nodules are numerous an extensive area of the lung may, by their presence, become in volved in a pneumonic process, so that the whole area, because of the filling of the air-cells with inflammatory material, added to the numerous solid tubercular nodules, becomes converted into a solid liver-like mass. This is spoken of as consolidation of the lung. A case of this sort will be difficult to distinguish from one of simple pneumonia, at least at first. But whereas in simple pneumonia the material filling the air cells liquefies in a few days and is expectorated, leaving the air-cells still intact, in that form of pneumonia which is really only an incident of the tubercular process, the breaking-down pro cess involves the lung tissue itself, and the recovery of the patient does not take place as in the simple inflammation. This might be called a tubercular pneumonia, but it is really only a type of consumption in which one feature has become prominent. In the same way the tubercles may by their situation cause conges tion and irritation of the bronchial tubes, and the prominent symptoms for a time may be of bronchitis only, such as cough and the expec toration of clear mucus, or cough only.
This is doubtless the explanation of numerous cases where the person is said to have contracted an ordinary cold, or to have had a severe chill, out of which consumption developed, the truth probably being that what was supposed to be the chill or common cold was really the early manifestation of the tubercular process itself. In the main, then, the chief features of the changes in the lung are : (1) the formation of the tubercular nodules, numerous or few, local ized in parts of the lung or scattered freely among its substance, (2) the conversion of these nodules into cheesy material—caseation of the nodules,—(3) the subsequent liquefaction and discharge of the matter, and hence (4) the for mation of cavities or (5) their conversion into fibrous patches by a process of cure, (6) the attendant inflammation of healthy lung tissue in the neighbourhood. The predominance of one or other of these features will determine the type of the disease and the character of the symptoms. The true nature of the dis ease when, because of the predominance of one symptom or another, it assumes at first the appearance of a pneumonia, a bronchopneu monia, or a bronchitis, will frequently be revealed by the discovery of the tubercular organism in the spit.
In some cases the progress of the disease may be slow, because of the less virulent nature of the organism, or the persistent resistance of the body in general or the lung tissue in particular. In such cases the tendency of the resistance of the lung takes the form of surrounding the tubercular nodule with a fibrous wall, limiting its growth and activity, and where this tendency has time to keep pace to some extent with the tubercular growth, considerable areas of lung substance may be converted into fibrous tissue.
This, though in a sense a process of cure, never theless destroys the true lung substance by re placing the air spaces by patches and strands of fibrous tissue, the shrinking of which still further compresses the lung tissue and destroys its capacity to expand with air. In such a case the ordinary symptoms of consumption may not be present, expectoration of matter, for instance, and way be replaced by increasing difficulty of expanding the chest and breathlessness, but it is still a variety of the same disease.
Similarly, tubercular nodules situated in the lung near the surface, or actually on the pleural lining, may produce by their irritation all the symptoms of a pleurisy, with or without effu sion, and a suspicion of the true character of the disease may only arise because of a long con tinuance of the disease and failure of the signs of recovery to show themselves at the usual time. Technically this would be a tubercular pleurisy, but the variety of the disease is only due to the accident, so to speak, of the situation of the tubercular nodules at the commencement of the illness.
The Tubercular Poison or changes that have been described are actual changes in the structure of the lung, of a destructive kind. But there can be no doubt that the tubercle bacillus, by its life and growth and activity, produces material foreign to the body, capable of acting as a tissue poison. Substances of this character can be detected in pure cultures of tubercle, so that though the broth or gelatin in which the organism has been grown may be freed from all living organisms by boiling and filtration, it is yet poisonous because it contains in solution products of the life of the bacillus. There is no doubt that some of the symptoms of tubercular disease are due to the poisonous effects of such substances, produced in the tissues where the bacillus is multiplying, and distributed to all the tissues of the body by the blood stream.
Infection of other expecto ration is infective, and, as might be expected, in its course upwards, through bronchial tubes, windpipe, voice-box, throat, and mouth, it may infect at any point. Thus ulcers occur in the walls of the air-tubes, on the vocal cords, or about the tongue and tonsils. Of, course all these parts may be the seat of tubercular ulcer ation due to deposit of tubercle upon them in the first instance. As a result of swallowing of the sputum, infection of the bowel is almost certain to occur sooner or later, and the whole digestive tract may be in a more or less ca tarrhal condition, due to irritation. Tubercular ulceration is commonest about the end of the small bowel. The growth of the ulcer may eat its way through the bowel-wall and set up a general and fatal peritonitis. Many cases of appendicitis are no doubt tubercular in origin, and bleeding from the bowel is frequently due to the erosion of a blood-vessel by the ulcerative process.