222 



SWINE DISEASES 



same time exert a positive chemotactic action upon the 

 leukocytes. In swine there is a very marked chemotactic 

 action and limited stimulation of connective tissue. 

 The typical porcine tuberculosis tubercle is largely com- 

 posed of leukocytes and has little fibrous tissue. 



Tubercles grow because of the increased accumulation 

 of leukocytes and the formation of a small quantity of 

 fibrous tissue. The tubercle contains no blood vessels; 

 that is, it is nonvascular, although in the early stages 

 there may be a hyperemic zone around the tubercle. 

 This hyperemic zone is the result of irritation in the tissue, 



Fiff. 27. TUBERCULOSIS OF THE SKIN. 



A. The skin showing: caseo-calrarous lesions. B. subcutaneous fat. 

 C. muscle. 



the tubercle formation causing a tissue reaction. As the 

 tubercle becomes larger, due to the accumulation of 

 leukocytes on the margin, the central part begins to 

 degenerate. 



Porcine tubercular lesions are characterized by en- 

 largement 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 produce increased 

 density of invaded soft tissues and are, therefore, easily 

 detected except in very recent infection. The tubercular 

 nobules in the early stages present about the same color 

 as the surface of the tissue invaded. In sectioning the 



