238 TUBERCULOSIS. 



and distribution. In most cases the lungs are affected, and contain numerous 

 rounded nodules, many being of considerable size ; these may be softened in 

 the centre, but are usually of pretty firm consistence and may be calcified. 

 There may be in addition caseous pneumonia, and also small tubercular gran- 

 ulations. Along with these changes in the lungs, the pleurse are also often 

 affected, and show numerous nodules, some of which may be of large size, 

 firm and pedunculated, the condition being known in Germany as Perlsiccht, 

 in France as ponimdiire. Lesions similar to the last may be chiefly confined 

 to the peritoneum and pleurae. In other cases, again, the abdominal organs- 

 are principally involved. The udder becomes affected in a certain proportion 

 of cases of tuberculosis in cows — in 3 per cent according to Bang — but 

 primary affection of this gland is very rare. Tuberculosis is also a compara- 

 tively common disease in pigs, in which animals it in many cases affects the 

 abdominal organs, in other cases produces a sort of caseous pneumonia, and 

 sometimes is met with as a chronic disease of the lymphatic glands, the so- 

 called "scrofula" of pigs. Tubercular lesions in the muscles are less rare in 

 pigs than in most other animals. In the horse the abdominal organs are usu- 

 ally the primary seat of the disease, the spleen being often enormously enlarged 

 and crowded with nodules of various shapes and sizes ; sometimes, however, 

 the primary lesions are pulmonary. In sheep and goats tuberculosis is a rare 

 occurrence, especially in the former animals. It also occurs spontaneously in 

 dogs, cats, and in the large carnivora. It is also sometimes met with in mon- 

 keys in confinement, and leads to a very rapid and widespread affection in these 

 animals, the nodules having a special tendency to soften and break down into 

 a pus-like fluid. 



Tuberculosis in fowls (avian tuberculosis) is a common and very infectious 

 disease, nearly all the birds in the poultry-yard being sometimes affected. 

 The relation of the different forms of tuberculosis is discussed below. 



From these statements it will be seen that the disease in ani- 

 mals presents great variations in character, and may differ in 

 many respects from that met with in the human subject. The 

 tubercle nodules may be of so large a size, e.g. in the horse and 

 ox, as to be described as sarcoma-Hke ; they may be tough and 

 firm, with little or no caseation, or they may be softened in the 

 centre, more resembling abscesses, or again there may be an 

 eruption of very minute granulations. However different their 

 naked-eye appearances may be, they are built up histologically 

 on the same plan, and of greater importance still is the fact 

 that they are all produced by the tubercle bacillus. An 

 account of the lesions experimentally produced will be given 

 later. 



Tubercle Bacillus. — Microscopical Characters. — Tubercle 

 bacilli are minute rods which usually measure 2.5 to 3.5 /u. in 

 length, and .3 ju. in thickness, i.e. in proportion to their length 



