INFECTIVE GRANULOMATA. 



351 



when the tubercle is from six to eight months of age and is ex- 

 tensive by the time the lesion is one year old. Tubercular masses 

 are occasionally observed in the lung, bronchial ur mediastinal 

 glands, and in the liver. These masses may contain all stages of 

 tubercular formation or the entire mass mav all be in the same 

 stage of devehjiMuent, as liquefying necrosis, cascatiun or calcifi- 

 cation. Tuberculosis of serous memliranes nf bnvincs should 

 receive special mention because of the characteristic appearance 

 of the lesions. Bovine serous membrane lesions varv in size from 

 a millet seed to a walnut, but arc usually aliout tlie size of a pea. 

 These lesions are freipicntly thickly studded over large areas of 

 a serous membrane. The nodules are surrounded l)v a firm cap- 

 sule \yliich causes them to appear as pearhHk'e 1)odies, ,:in(l !i,:-i;rr 



Fig. 196. — Photograph of a tubercular manimar.v gland, i-ix 



the name, "pearly disease.'' Sometimes serous membrane tuber- 

 cular lesions are very extensive; this type may be called "mass 

 tuberculosis." 



Porcine Tnbcradar lesions are characterized by enlargement of 

 lymphatic glands, the formation of tubercles of variable sizes in 

 or upon serous membranes and within the substance of glandular 

 organs, bones and other connective tissues. The tubercles pro- 

 duce increased density of invaded soft tissues and are, therefore, 

 easily detected except in very recent infection. The tubercular 

 nodules in the early stages present about the same color as tlie 

 surface of the tissue invaded. In sectioning the tubercle the cen- 

 tral portion is caseous and slightly yellow or fibrous and white. 



