TUBERCULOSIS. 517 TUBERCULOSIS. and white blood cells. The 'tul)erclc,' which is now fully developed, inaj- next underyii dcj;eiieia- tive changes consisting of either caseation or sclerosis. Caseation begins in the centre of the growth and consists in a degeneration of the cells and their reduction to a honiupeneous. struc- tureless mass. Coincident with the caseation or following it is a sclerosis by which the tul)ercle is converted into a firm, hard substance composed of connective tissue rich in fibres. Osier describes very graphically these two processes as follows: '"In all tubercles two processes go on: one — casea- tion — destructive ami dangerous; and the other — scleroses — conservative and healing. The ulti- mate result in a given case depends upon the capabilities of the body to restrict and limit the growth of the bacilli. There are tissue soils in which the bacilli are. in all probability, killed at once — the seed has fallen by the wayside. There are others in which a lodgment is gained and more or less damage done, but finall}' the day is with the conservative protecting forces — the seed has fallen upon stony ground. Thirdly, there are tissue-soils in which the bacilli grow luxuriantly, caseation and softening, not limita- tion and sclerosis, prevail and the da.v is with the invaders — the seed has fallen upon good ground." Small tubercular nodules are called miliary tubercles. Seen with the naked ej'e the nodular tubercle is a small white, gray, or yellowish body, the smallest not visil)le without a miscroscope. Microscopically these tubercles show around their edges proliferated connective tissue and endo- thelial cells, with often some giant cells, while the centre is composed of tissue undergoing caseation or coagulation necrosis. Tubercle ba- cilli may be few or numerous. Diffuse tubercle tissue usuall,v results from a rather extensive local infection resulting in many small foci near together. From these tubercles start to grow, and these coalescing form consid- erable areas of tubercle tissue. In addition to the formation of tubercles the bacilli or the pres- ence of the tubercle tissue may set up secondary inflammatory processes. Suppuration in connection with tubercular in- flammation frequently occurs. In the .so-called 'cold abscess,' however, the fluid is not, properly speaking, pus, but the products of breaking down of the tuliercles. The question as to whether the tubercle bacillus alone is capable of causing sup- puration is still debated. It seems probable, however, that most cases of suppuration in tuber- cular conditions are due to what is known as 'mixed infection,' that is, the presence of pyo- genic cocci with the tubercle bacilli. Acute general miliary tuberculosis is charac- terized by a ra|iid devehipment of tubercles, usu- ally of small size, in many parts of the bod.v at about the same time. The number of tubercles is frequently very large. One of the explanations offered for such siulden general diffusion of tu- bercles is that the infection is secondary to tuber- cles located in the walls of some of the small blood vessels or lymphatics. Pulmonary tuberculosis, tuberculosis of the lungs, lung consumption, or. most commonly called simply 'consumption.' is a form of tuber- cular infection in which the only or the most prominent lesions are in the lungs. The bacilli usually gain entrance by being taken into the lungs with the inspired air. Less commonly in- fection of the lung may occur through bacteria being brought to them by ncans of the blood or lympli cluinnels from tubercular foci in other parts of the body. Several factors nuist be con- sidered as determining the character of the in- flammation which the tulicrcle bacillus may induce in the lungs. Among these may bo men- tioned the number of bacilli introduced, their virdence, the numner in wdiich the}- enter the lungs, whether in respiration or by means of the blood or Ijmph, the susceptibility of the indi- vidual, etc. As a result of variation in these factors we find a variation in the character of the inllanimation set up. Thus there may result an exudative inflammation in which the air spaces of the lung and the smaller bronchi are filled with serum, leucocytes, fibrin, and cast-ofl' epi- thelium. Such reaction is quite similar to that induced by the pneumococcus in pneumonia. On the other liand, instead of an exudative inllamma- tion, the tubercle bacillus may bring about the production of new tissue, that is a productive inllanunation. This new tissue is composed of small round cells and epithelioid cells, such as have been described above as tubercle tissue. In some cases there is death or necrosis of lung tis- sue with the formation of abscesses. While it is couutRJU for these different lung- tissue reactions to tubercular infection to be as- soiiated, the predominance of one or another allows us to differentiate several quite distinct tyjies of tuberculosis of the lungs. AciTE MiLi.RY Tuberculosis of the Lungs. This occurs usually as a part of a general miliary tubei'culosis, although it may be difficult to find lesions in other organs. The tubercles v.irv in size and are found in both lungs, lying in the hmg tissue proper, in the walls of the vessels and bronchi, or in the connective-tissue septa. They may be quite evenl.y scattered or distributed in groups. The structure of the tubercles has been already described. The tubercles undergo coagulation necrosis, and there is apt to be some iuflannuatorv reaction in the adjacent air spaces, as evidenced b.v more or less exudation. Some of these tubercles may be of considerable size, but many of them are often too small to be visilile to the naked eye. These tubercles may go on to suppuration. They may coalesce to form larger tubercles. On the other hand, instead of breaking down, the tissue is sometimes converted into masses with or without calcified centres. These are known as 'healed tubercles,' and ma,v or may not contain tubercle bacilli. Tuberculous Broncho P.EuifONi.. In this form of tuberculous infection of the lungs, the tuberculous areas occur in the walls of the small- er bronchi and in the contiguous lung tissue. In its early stages the inflammation is mostl.v catar- rhal, there being a more or less extensive exudate into the affected bronchi. As more and more bronchi are affected, there is frequently a coales- cence of adjacent areas, with the formation of quite large mas.ses of consolidation. These break- ing down form cavities. The progress of the affection may be slow or rapid, and is one of the forms of pulmonary tuberculous popularly called ■phthisis.' The term 'phthisis' is also applied to diffuse exudative tuberculous inflammation of the lungs, which may be either acute or chronic. In the acute form extensive areas of hmg tissues may
