MORBID ANATOMY 



139 



in shape owing to their 

 mutual pressure (Fig. 

 31). Sometimes these 

 tubercles are attached to 

 the serous membrane by 

 a small, tough, fibrous 

 pedicle ; frequently, how- 

 ever, this is absent and 

 the nodules rest bodily 

 upon the membrane. 



The structure of the 

 tubercle consists, in the 

 beginning, of a few cells 

 surrounding the invad- 

 ing specific organisms. 

 These are soon encased 

 by a zone of epithelioid 

 cells and giant cells 

 which is soon sur- 

 rounded by an outer 

 layer of round or lym- 

 phoid cells. The central 

 portion becomes necrosed 

 and as the nodule en- 

 larges the central ne- 

 crotic portion becomes 

 correspondingly large. In 

 cattle there is a strong 

 tendency for the necrotic 

 tissue to become infil- 

 trated with lime salts 

 and encapsulated (Fig. 



Fig. 26. Trachea and bronchial 

 tubes of bovine lungs showing at- 

 tached bronchial glands. a. a., supply 

 right afid left caudal lobes, b.b., supply 

 r. and I. ventral lobes. c-c\ branches of 

 its right supernumerary bronchus. C-, sup- 

 ply left cephalic lobe, d, branch to azygos 

 lobe, e, trachea. A, left bronchial lymph 

 gland. B, right bronchial lymph gland. 

 C, lymph gland base of supn . bronchus. D, 

 gland often between bronchi. The glands 



A. to D.are often involved. (Smith.) 

 32). In certain other species a deposit of fibrous tissue in 

 the outer zone of the tubercle has been observed. In the 

 smaller and more susceptible experimental animals such as the 

 guinea pig and rabbit and frequently in swine, the lesions are 

 of a more diffuse nature infiltrating the interstitial tissue with 

 the tuberculous mass and gradually encroaching upon the par- 

 enchyma. Circumscribed tubercles may also be present. 



